For utilization of flyash which is one of byproducts, authors focus on flyash cement having relative lower consumption, even specified in JIS. One of the reasons for lower consumption is slower early strength development than ordinary Portland cement (OPC) in case of much replacing ratio of flyash in flyash cement. Therefore in this study, strength enhancers as cement additives are studied on the effect of strength development, especially for early age. Firstly, the compressive strength of mixtures using OPC and flyash corresponding to JIS Type-B and Type-C are measured to confirm the effect of the strength enhancers. Additionally, the heat of hydration by isothermal calorimeter of cement paste using amines as strength enhancers are measured for discussion of the effect of the strength enhancer for cement hydration and the hydration mechanism for early strength enhancement. The conclusions are as followings;
1) Two different strength enhancers Triisopropanolamine (TIPA) and Alkanolamine are evaluated for FA Type-B-mixture and FA Type-C-mixture replacing flyash to a part of the OPC. Alkanolamine shows higher strength than TIPA by FA Type-B-mixture and FA Type-C-mixture. Besides, Alkanolamine shows higher strength than OPC from 1day to 7days. This result shows the effect of strength enhancer differs for mixtures, and it suggests that TIPA and Alkanolamine have different hydration mechanism. 2) As a result of heat of hydration, Alkanolamine generates highest heat of FA Type-B-mixture and FA Type-C-mixture. The strength enhancers are considered to have acceleration effect for this heat of hydration. 3) In dissolution test using flyash and the strength enhancers, TIPA shows high elution amount of Fe2O3 from flyash. In contrast, Alkanolamine shows no effect for dissolution of Fe2O3. But when using TIPA and Alkanolamine for flyash, it was confirmed that the amount of effusion of the metal-ion was different than only flyash mixed. 4) C3S or C4AF is used for heat of hydration measurement to determine the hydration mechanism of the strength enhancers. Alkanolamine shows acceleration effect for C3S. However, TIPA shows the retarding effect constantly. For C4AF, Alkanolamine shows higher acceleration effect than TIPA. 5) As for estimated hydration mechanism for early strength enhancement, the strength enhancers would accelerate C3S and C4AF in OPC.
In the Great East Japan Earthquake 2011, a large number of buildings collapsed and the strength of ceiling boards using plaster finishing was occurred as serious problems as a possible problem. That is why, since the Great East Japan Earthquake, the owners of old buildings are concerned about the deterioration of the building components. Therefore the number of owners seeking to strengthen their building's components have been increasing day by day. Moreover, in addition to preserving these historical buildings, it is also necessary to secure the safety from the standpoint of cultural and historical values. Therefore, we focused on these wood lath and plaster ceiling that's used as a target of evaluation for saving the historical building. In this study, an experimental study of inspection of an existing wood lath and plaster ceilings, we evaluate the strength and other properties of plaster, and finally conduct the objectives to prolong the duration of life with safety conditions. Plaster materials have frequently been used in old building's ceilings and walls. In general, the role of plaster ceilings are to transfer stress buffering between the lath and plaster. Therefore, it is important for the lath and plaster to be strongly adhered. This portion has been called Plaster Key in general and its role is to evaluate the mechanical properties of the plaster ceiling and wall. In Japan, this type of ceiling using plaster and mortar has been used from the early 1900s, and over a century has passed since the lath and plaster ceilings were developed, and at the same time the plaster has frequently been damaged in earthquakes. The two specimens used in experiments were cut from a renovation ceiling of Morioka bank (built in 1911). One of the ceilings has been constructed at the same time as the construction of the bank at 1911. The other ceiling has been constructed when taller buildings were being constructed in the 1930s. The experiments are the evaluation of wood lath specification, image analysis from the attic and hammering test for the plaster surface finishing. The space of the wood lath of 1911 was more than 10mm length, and plaster keys were formed solidly. In addition, the timber around the lath were stable in both thickness and width. On the other hand, the specimen of the 1930s was two times as big as the 1911 specimen. Additionally, the gaps of the wood lath were less than 10mm wide. Therefore, the plaster ceiling was heavy and there were significant influences to the plaster layer exfoliation. Image analysis can be evaluated in a non-destructive manner the health of the traditional member by photos and sighting survey from the attic. Therefore, this method is particularly effective in the traditional member which is difficult to change the design and material. The strength of the ceiling at 1911 had a locally small part of plaster surfaces and was shown that the relative strength was smaller than average strength. The peak value of the strength of the 1911 was smaller than that of the 1930s. Thus, this means that the plaster of the ceiling had already been fragile, and when the peeling and falling of the plaster layer, the broken unit and particles were assumed to become small pieces. On the other hand, the hammering test results of the specimens from the 1930s were stable and small variability. The reason is that the thick plaster layer and high rigidity. Our results showed that non-destructive soundness evaluation of wood lath and plaster is reliable.
Information about possible existence and its extent of structural damage is extremely important to diagnose structural health. The damage detection methods based on change in the building characteristics before and after the earthquake have been studied for a long time. However, the characteristics of the whole building system such as natural frequency have problems with ambiguity of relationship between characteristic change and damage state, and also sensitivity to local damages. To solve these problems, some authors have proposed a local damage detection method focusing on the characteristic change of each substructure, and have been doing analytical and experimental studies. A major obstacle to practical application of the method is that a large number of measurement points (sensors) are required, but recent innovative advancements of sensing technologies will allow us a large number and high density sensor deployment to the building. In order to experimentally verify the proposed substructure-based local damage detection method, it was applied to the large shaking table test of 1/3 scaled 18-story steel high-rise building in December 2013 at the E-Defense. A multi point time synchronous data measurement system with 152 MEMS-type six-axis vibration sensors was developed. The sensors were deployed to each beam-to-column joint of the test building to measure its translational acceleration and rotational velocity. The proposed local damage detection method was applied to the measured data for the existence and extent of local structural damages in each test stage to be estimated. The damage detection results were compared with the actual status of the test building to evaluate the performance of the proposed method. As the conclusion of this paper, the following three points were shown from the experimental results. 1) The multi point time synchronous measurement system experimentally demonstrated that six-axis vibration at all beam-to-column joints of the 18-story steel high-rise building (152 sensors × 6 directions = 912 ch.) can be synchronously measured at 500 Hz. It was confirmed that vibration in the rotational direction can be measured with enough accuracy and its amplitude is sufficiently large with respect to the resolution of the MEMS sensor (0.0125 deg./s) 2) The practical damage detection method based on the output error of the substructure was presented as a damage index Di which is the normalized amplitude of output error increase to an initial state of the substructure into consideration of the influence of observation noise and modeling error. As a result of the verification based on the experimental data, the damage detection could be performed using a single threshold value for all substructures even to the data set with different amplitude levels. 3) It was verified that the damage detection result of the proposed method at each stage of the experiment is in good correspondence relationship with the distribution of flange fractures at the steel beam ends as the actual damage status of the test building. As a result, it was proved that the local damage distribution of a steel rigid frame structure can be estimated by the proposed method.
The behavior of pile foundation during earthquake is affected by soil-pile-building interaction and its nonlinearity. When we calculate the pile stress, the nonlinearity of soil material should be considered. For failure criterions which can express nonlinearity of soil, Mohr-Coulomb failure criterion and Drucker-Prager failure criterion are used. However, the influences on soil resistance around piles caused by the difference of these failure criterions are not clear yet. On the other hand, horizontal soil resistances in pile groups are affected by the interaction between piles, which is called the effect of pile groups. In our past researches, we have analyzed about soil resistances around each pile in pile groups in sandy soil, but we have not discussed the case of cohesive soil. The failure criterion of cohesive soil is different from sandy soil. This difference may affect the behavior of pile groups. Therefore, it is necessary to discuss soil resistance of a pile group in cohesive soil. This paper discusses the influences on soil resistance of a pile group caused by different failure criterions. Nonlinear static analyses on the 25-pile groups were performed using 3-dimensional finite element method. The piles are steel pipe piles with a length of 11m and a diameter of 600mm. The pile group is arranged in a 5x5 pattern. Each pile is located with center-to-center spacing of 1.5m. Soil parameters of internal frictional angle and cohesion are mainly discussed. Both springs at the pile head and around pile shaft are calculated. When calculating the spring at the pile head, the piles are modeled by the elastic shell elements and forced displacement is given to the pile head. When calculating the soil spring around the pile shaft, the piles are modeled as the excavated ground and uniform forced displacement is given to the whole of the piles. The major conclusions of this paper can be summarized as follows: 1) Under the Mohr-Coulomb failure criterion, the strength of sand differs between triaxial compression and triaxial tensile. The difference determines the subgrade reaction of piles. Near ground surface, the subgrade reaction is determined by the strength under triaxial compression, while in deeper parts of the ground, the subgrade reaction is determined by the strength under triaxial tensile. 2) In the case of sandy soil, subgrade reaction concentrates on front piles in a pile group. While in the case of cohesive soil, the concentration on front piles is softened by side piles. 3) Concentration ratio of the subgrade reaction is discussed. In sandy soil, concentration ratio on front piles goes higher with the growth of displacement, while the concentration ratio of side piles gets lower. But in cohesive soil, concentration ratio of front piles and side piles hardly change with displacement. 4) Both in sandy soil and cohesive soil, the subgrade reaction concentration ratios on front piles and side piles get lower near ground surface. While in deeper parts of the ground, they are almost constant values.
The objective of this study is to examine the concrete filled effect in the hollow part of SC pile in order to improve the deformation performance of pile. In the pile foundation structure, the improvement is prompted, assuming secondary seismic design. But, Study on the deformation capacity of precast concrete pile is not sufficiently advanced. The bending tests of plie are carried out on a daily basis for performance assessment. The purposes of the test is the confirmation of the flexural strength. Therefore, the test data accumulation is not enough to discuss the deformation performance of pile. This study focuses on the SC pile in precast concrete pile. The SC pile is a cylindrically shaped member manufactured by centrifugal casting with concrete placed in the hollow section of a steel pipe. The SC pile is a composite pile that utilizes the merits of concrete with good resistance against compressive forces and steel shell with good resistance to tensile forces. Concrete prevents local buckling of the steel pipe, while the steel pipe constrains concrete; therefore, the SC pile has excellent flexural bearing capacity and deformation capacity. This study examined effects of some parameters for deformation performance of the SC pile by the simple beam bending test. Four parameters are set for the test. The parameters are 1) Loading method, 2) Steel pipe thickness, 3) Axial force, 4) Infilled material. We observed the failure conditions, relations between the load and the displacement, and relations between the bending moment and the curvature. The knowledge obtained from this study are shown below.
1) Reinforced by infilling the hollow part of the pile with material, the following effects can be expected: prevention of depression of the steel pipe, prevention of flaking or crush of the pile body concrete, and improvement of the bending deformation performance of the pile. It is more effective to use infilled material with high Compressive strength and high Elastic modulus.
2) The results of bending tests of piles, maximum flexural strength and maximum curvature, are influenced by loading method. The results obtained by the one-way cyclic loading are greater than those obtained by the peak-to-peak alternate cyclic loading. Test value obtained by the one-way cyclic loading is on dangerous side as the evaluation of the deformation performance of the pile. Therefore, it is desirable to adopt the peak-to-peak alternate cyclic loading for appropriate evaluation of the deformation performance of the pile.
3) It is effective to increase the thickness of the steel pipe for the improvement of the flexural strength of the pile. But, it is not effective to increase the thickness of the steel pipe for the improvement of the deformation performance of the pile.
4) With respect to the maximum value of curvature, the test value of the standard specimens is not more than the analysis value. The test value of the test specimen that was reinforced with soil cement is about equivalent to the analysis value. The test value of the test specimen that was reinforced with concrete is greater than or equal to the analysis value.
In the 2011 off the Pacific coast of Tohoku Earthquake, many suspended ceilings and other suspended equipment fell down due to the lack of their resistance to earthquakes. To mitigate severe damage to ceiling system caused by earthquakes, new seismic design code for suspended ceiling system was issued by the Ministry of Land, Infrastructure, Transport and Tourism. However, the mechanism why and how suspended ceiling system falls down during earthquakes has not yet been clarified well. In order to clarify the collapse mechanism of wide-area ceiling system and development of its countermeasure, new research project was launched and the first series of full-scale shake table experiments of wide-area ceiling system in school gymnasium was conducted. This paper presents outline of the full-scale shake table experiment and global response of structural members. The specimen was designed as the full-scale specimen which can represents real steel school gymnasium on spread foundations built in elementary and junior high schools based on the allowable stress design with base shear coefficient C0 of 0.2. It had a floor plan dimension of 30m by 18.6m and a height of 9.09m. Because its size was larger than the shake table size of 20m by 15m, it was supported by cantilevered large stiff girders with the overhang of 5m at the maximum. Based on pushover analysis using Ai distributions, it was confirmed that the base-shear versus displacement relation in the specimen was close to that in the prototype of the specimen. In the specimen, two different types of suspended ceiling were installed; 1) non-seismic ceiling and 2) seismically designed ceilings with seismic coefficient of 1.1G and 2.2G. Fail-safe system consisting of wires and nets to prevent damage caused by suspended equipment to people inside the gymnasium was also installed to evaluate its effectiveness. Two ground acceleration records were used as imposed motions; 1) K-NET Sendai record observed at K-NET Sendai station during the 2011 off the Pacific coast of Tohoku Earthquake and 2) JMA Kobe record observed at JMA Kobe observatory during 1995 Hyogo-ken Nanbu earthquake. Intensity of imposed motions were 5%, 25% and 50% (twice) of K-NET Sendai record for the specimen with non-seismic ceiling and 5%, 25%, 50%, 80% and 100% of K-NET Sendai record and 100% and 150% of JMA Kobe record for the specimen with seismically designed ceilings. Based on the shake table experiment, it was found that response accelerations measured at the base of corner columns (the edge of cantilevered stiff girders) were close to the original record in horizontal directions while vertical response accelerations were amplified in the frequency of 10Hz. It showed the response acceleration should be carefully checked in high frequency components. Based on the whitenoise excitations, natural periods and mode shapes were estimated. It was clarified that the vertical response was coupled with horizontal response and the intensity of vertical response was the maximum value of 32% of the intensity of horizontal response. Based on the excitations using K-NET Sendai and JMA Kobe records, the maximum response displacement at the roof top was 2.05% (=1/49) and 4.47% (=1/22) of the height of specimen in span and ridge directions, respectively. Only the base of columns yielded, however, no damage was observed in columns, girders and beams. All vertical and horizontal braces yielded and buckled repeatedly, and the deformation in the out-of-plane direction was observed. However, no brace ruptured.
It is known that Japan has entered a period of brisk seismic activity starting with the 1995 Hyogo-ken Nambu earthquake. The past earthquakes caused collapse of a lot of traditional wooden houses and human suffering in various parts of Japan. Therefore, it is important to conduct appropriate seismic evaluation and reinforcement to improve the seismic performance of the houses. On the other hand, the calculation method of response and limit strength is often used in reinforcement design of traditional wooden houses which have low strength relatively. However, the structural characteristics of traditional wooden houses, such as a) uplift of columns adjacent mud walls, b) reverse shear force of through columns, c) slide of column bases, d) breakage of through columns and joints by shear resisting elements local in a plane structure, are difficult to be taken into account by the calculation method regularly used in reinforcement design of traditional town houses, machiya, in Kyoto. Therefore, we thought that it is very effective and important to demonstrate seismic reinforcement of traditional wooden houses. In particular, machiya in Kyoto have typical plane frames and ripple effect is expected by effective reinforcement examples of the typical plane frame. From the above, in this paper, we demonstrate the effect of the seismic reinforcement of machiya in Kyoto by the experiments and the simulation analyses. First, we conduct the static loading tests of the unreinforced and reinforced plane frame structures of the typical two-storied machiya in Kyoto. Then, we analyze the difference of the restoring force characteristics and the damages between the unreinforced and reinforced frames. Finally, we simulate the static loading tests with the analysis models to confirm the effect of the seismic reinforcement in detail and whether we can detect the undesirable seismic reinforcement method using the simulation analyses. The major findings obtained from the research are summarized as follows: a) In the frame which has a wall only in the first story, the deformation angles of the first story and the second story become uniform by adding a wall to the second story. As the result, the damage of the through columns and the joints decreases and the reverse shear force of the through columns goes down. Besides, the rocking deformation of multi-story walls is expected to increase the deformation performance of the whole frame structure. b) The increase of the stiffness and the strength of the local part in the frame is possible to cause breakage of the through columns or falling of the beams at the early stage. c) When the slide of the column bases is concerned, the reinforcement by bridge batten of foot columns which restrains the increase of the distance between the column bases is effective, because the increase of the distance between the columns is possible to cause falling of the beams. d) Except for the frame whose beam pulled out from the column and fell in the experiment, the analysis models of the frames which neglect the pull-out of the joints can explain the restoring force characteristics of the test results. e) The modeling of the pulling-out resistance of the tenon of the beams has a large effect not only on the pulling-out deformation but also on the bending moment and the restoring force characteristics of the frame.
The important structural elements of traditional timber structures in Japan are rotational resistances of column-beam joints. The restoring forces characteristics of their structures depend on the rotational resistances of the joints. Therefore, the elasto-plastic restoring force characteristics of embedment of joints is the most significant in order to evaluate the seismic performances of the traditional timber structures. The authors have already applied Pasternak Model (abbreviated to PM) to the embedment and established the formulation of embedment mechanisms of partial compression of wood, which is the most appropriate embedment mechanical model for embedment problems. Furthermore, they developed the Elasto-plastic Pasternak Model (abbreviated to EPM) for the elasto-plastic embedment mechanism considering the strain hardening behavior. However, there are many types of joints and their resisting mechanisms are different. Thus, the mechanisms of different types of joints should be made clear. The authors have already established the formulation of crosspiece joint applying the EPM of the mechanism and confirmed the formulation based on the static loading tests. In this paper, the authors focus on the strut which has not been considered as a structural element so far, and propose the formulation of embedment mechanism of the strut, as a model of rotational embedment under the constraint conditions. Then, they carried out loading tests of the struts, and obtained their restoring forces characteristics. The loading test of two types of struts were carried out; one is Y-series (six specimens) which support the floor beams standing on the base stone. The other is T-series (three specimens) which stand between two beams, called, “Taihei tuka”. The dimentions of the strut are: depth:120mm, breadth:120mm, height:280mm. Beams depth:180mm(Y-1～3) and 90mm(Y-4～6), and 150mm (T-1～3). All species of specimens are Japanese cedar (Sugi). The test results showed that the maximum horizontal resistances of Y-1～3 were 8～11kN, the maximum normal loads were 36～50kN. The maximum horizontal resistances of Y-4～6 were 6～7kN, the maximum normal loads were 18～28kN. T-1～3 were the maximum horizontal resistances of 12kN, the maximum normal loads were 48～53kN and had the large deformability up to 200mm. The resisting mechanism of strut joints due to horizontal loads is “Diagonal Effect” which push up the beam, rotating and embedding into the beam in accordance with the rotation of the strut. The mechanism is due to geometrical fact that the diagonal line of the strut is longer than the height of the strut. Another mechanism is the distance between beams decreases due to inclination of column. The same mechanism is found in short beams between inclined columns and panel walls within the frames. The authors considered the mechanism of struts is rotational embedment of strut into beams under the constraint conditions and proposed Elasto-plastic Pasternak Model formulation established by the author, in order to analyse them appropriately. Then the formulation is discussed and verified by the simulation based on the Elasto-plastic Pasternak Model formulation. As a result, the deformability is very large and the strut should be considered as a structural element for exact seismic estimation of traditional timber structures.
On October 15, 2013, Bohol Island locating in the central region of the Philippines experienced an earthquake whose magnitude was 7.1, and a number of reinforced concrete (RC) buildings were seriously damaged by the earthquake. This study focuses on an RC building which was damaged by the earthquake because of no hoops in the beam-column joints. The damage was observed to the exterior beam-column joints. Such RC buildings with poor joints are likely to exist worldwide especially in developing countries; thus, practical strengthening methods need to be developed. This study proposes a method to strengthen and rehabilitate exterior beam-column joints by installing RC wing walls, and presents the design procedure for wing walls installed to prevent the beam-column joint failure. A series of experiments using three specimens was conducted to verify the effectiveness of the proposed method. Three 1/2.5-scale exterior beam-column joint specimens representing the earthquake-damaged building in Bohol Island were prepared, and the seismic performance and behavior of the specimens were evaluated under reversed cyclic loads. One of the specimens without the strengthening was the control specimen (J3) to observe the behavior of the existing frame. Another specimen was strengthened by installing wing walls before the test (J3-WI). The other specimen (J3A) was subjected to preliminary loads up to a deformation at the maximum strength before the strengthening, and then it was rehabilitated by installing wing walls (J3A-WI) and loaded in the same way as the other two specimens. The wing walls were designed to prevent joint failure by reducing the moment applied to the joint; the joint moment was reduced by tension/compression from the pulled/pushed wing wall to the adjacent beam. The un-strengthened control specimen J3 failed at the joint and a story yield mechanism was formed in the second story. The observed behavior was brittle and the damage was similar to that of the focused building. The strengthened specimen J3-WI showed ductile behavior forming a beam yielding mechanism. The rehabilitated specimen J3A-WI also behaved in a similar manner, however, the strength deteriorated under cyclic loads beyond a drift angle of 6% rad. This was caused by a loss of bond between concrete and beam longitudinal bars in the existing beam-column joint where the preliminary damage was applied as mentioned above. The experimental results verified that the strengthening method of installing wing walls beside existing columns was effective to upgrade the seismic performance of existing beam-column joints without hoops by shifting the failure modes from brittle joint failure to ductile beam yielding. However, when wing walls are installed into damaged frames, they should be designed considering deterioration of bond between concrete and beam longitudinal bars in the existing joint.
In the seismic retrofitting of an existing concrete structure, the surface of the structural frame is chipped to improve the integrity between the existing frame
and retrofitting member. But, quantitatively evaluating strength of these joints are difficult because the concavo-convex shape is influenced by construction
worker. Therefore, the authors developed a new joint referred to as the cylindrical shear-key. The cylindrical shear-key is made by filling a cylindrical core
on the concrete surface with grouting mortar or concrete, and resists shear forces as a shear-key. Creating a uniform shape is expected to enable quantitative
strength evaluation. In this study, direct shear tests were conducted using a cylindrical shear-key to investigate the fundamental performance of the shear-key.
Then, based on the test results, an equation was developed for evaluating the strength of cylindrical shear key, and it was shown that the maximum strength
could be quantitatively evaluated accurately. And cylindrical shear-key is can contribute to the progression of seismic retrofitting.
Seismic performance of flexure-dominant reinforced concrete walls with deformed bars at crack control joints as crack inducers is experimentally and numerically investigated. Deformed-bar-crack-inducers have been proposed for use in structural walls in mid-to-high-rise housing complexes. A couple of half-scale two-story RC wall test specimens were constructed on a stiff base foundation. They had boundary columns at both sides with a stiff girder at the top for loading. The wall in each story was 1100 mm high, 2200 mm long, and 100 mm thick. The thickness was reduced to 80 mm at the crack control joints, two of which were located at the boundary between wall and columns, and one of which was at the mid-span. The test parameter was the diameter of the crack-inducing bars; type D6 for test specimen FWP63R07 and type D16 for FWP63R20. The nominal compressive strength of concrete in design was 30 MPa and longitudinal reinforcements of the beams and columns were type SD345. The other reinforcing bars were type SD295A. To design the walls not to fail in shear, the ultimate shear strength of the walls was 1.91 times greater than the ultimate flexural capacity without considering the reduction in the wall thickness at the crack control joints. While the two boundary columns were subjected to 1080 kN as the axial load, the lateral loading was applied at the mid-span of the top beam. By using the finite element analysis program DIANA9.6, a detailed numerical study on the structural response of the walls such as load-drift angle relationship, stress-strain distribution of the crack-inducing bars, stress distribution of the deformed bars, and the vertical displacements of the boundary columns' bases was carried out as well. The following conclusions can be drawn from the experimental and numerical works of this study. (1) The crack-control joints at the boundary columns' faces did not contribute to the overall collapse mechanism. (2) At drift angel by 0.5% the two test specimens exhibited identical load-deflection relationships. No influence of shrinkage cracks and bar diameters were found. (3) The test specimen with type D6 crack-inducing bar reached its ultimate strength at R=1.5% while the other test specimen with larger crack-inducing bar diameter (type D16) exhibited its ultimate strength at R=1.0%. It seems that the difference in crack-inducing bar diameter could contribute to such a discrepancy. (4) It was found that the crack-inducing bar diameter had no influence on the vertical sliding displacement of the crack-control joints. (5) It was found the conventional equations can be applied for evaluating the initial stiffness, flexural cracking strength, and the bending ultimate strength of the wall test specimens when neglecting the wall cross-section reductions at the crack-control joints. (6) The predicted ultimate flexural strength of the two test specimens was approximately 20% smaller than the test results. (7) The developed finite element model in this study could simulate the lateral load-deflection of the test specimens until almost the ultimate capacities, the vertical displacement of the walls' bases before reaching the tensile rupture of their longitudinal reinforcements, and the strain distribution of the crack-inducing bars at R=0.25%. By verifying the test and FE results, a series of parametric studies investigating the influence of crack-inducing bar diameter, number of crack control joint, wall reinforcement ratio, and concrete strength is under development.
1. Introduction We have proposed a hysteretic damper of tubular shaped steel in order to adapt to anchor bolts of exposed bases in steel moment frames. The damper is expected to deform stably over a large plastic deformation range in the axial direction after local buckling occurs. In the previous research, cyclic loading tests of exposed bases with the dampers have been conducted. The test results reveal the technical viability, however there is a problem that the deformation capacity decrease caused by insufficient of the shear stiffness and strength. The present paper describes the loading tests for exposed-type column base with the dampers using different shear resisting mechanisms. Moreover, the evaluation method of the deformation capacity is proposed.
2. Loading tests The number of specimens is six. The parameters are sizes of the tubular dampers and shear resisting mechanisms. force are employed as the shear resisting mechanisms. The specimens are loaded cyclically with incremental deformation amplitude under constant axial force. The test results show that the deformation capacity of the specimen with the concrete floor slab is higher than any other with the shear key. This is because the concrete floor slab can bring the highest shear stiffness In case of the specimen with carrying high compressive force, shear stiffness deteriorated because the grout under the base plate collapsed.
3. Evaluation of deformation capacity The test results confirmed that the bending shear deformation of the dampers correlate highly with the shear stiffness of the resisting mechanism. In order to evaluate the deformation capacity of the tubular dampers, an influence factor to consider the bending shear deformation is introduced. The method to evaluate the deformation capacity with the regression formula for the factor is proposed.
4. Conclusion The main conclusions are summarized as follows: 1) In the case of the specimens with concrete floor slab for shear resisting, the deformation capacity was the highest among the specimens in the loading tests. 2) The method to evaluate the deformation capacity with the empirical formula is proposed.
Braced frame structures are used for low-rise steel buildings with large space such as school gymnasium, and angle braces are often adopted as the main seismic component. These buildings are used as emergency public shelters in event of disaster. Therefore, it is very important to secure the sufficient seismic performance. However, a reconnaissance of the recent earthquake reports that the brittle fracture at the effective cross-section of an angle brace. Single-angle brace has the inevitable eccentricity between the brace and its gusset plate, and this detail is a disadvantage in terms of connection strength. Therefore, in the case of double-angle brace, it is known that the removal of the out-of-plane eccentricity leads to the improvement of the ultimate strength at the effective cross-section. In addition, the previous paper reports that Z-shaped double-angle brace removing both out-of-plane and in-plane eccentricities brings further increase in the ultimate strength at the effective cross-section. On the other hand, the recent studies on double-angle brace point out the decrease in cyclic deformation capacity. A purpose of the present study is to clarify the effect of connection detail on not only strength at the connection but also cyclic deformation capacity of angle brace. In the present paper, both connection tests and component tests were carried out. Specimens of the tests are angle braces connected to gusset plates using high strength bolts. In the connection test, the monotonic tensile loading was employed in order to investigate the effect of connection detail on the ultimate strength. The main parameters were angle cross-section (L65x6, L75x6 or L90x7), thickness of gusset plate (PL9, PL16 or PL19), connection detail (single, double-angle or Z-shaped) and the number of bolts (2 to 5). On the other hand, in the component test, the cyclic loading was employed to verify the influence of connection detail on cyclic deformation capacity of the angle braces. The test parameters were angle cross-section, thickness of gusset plate (PL9, PL12 or PL16), connection detail and loading protocol (incremental or constant amplitude). The result of the connection tests indicates that the effective yielding leg ratio of single-angle brace is independent on the number of bolts, which are approximately constant at about 0.5. However, those of both double-angle and Z-shaped double-angle brace increase in proportion to the number of bolts, whose values are roughly from 0.2 to 1.1. Therefore, it is found that the out-of-plane eccentricity has a great influence on the yield strength at the connection of angle brace. Meanwhile, the ultimate strength at the effective cross-section tends to increase in proportion to the number of bolts. However, the effective leg ratio of the cross-section of both double-angle and Z-shaped double-angle brace is 1.2 times to that of single-angle brace. It means that the removal of out-of-plane and/or in-plane eccentricity has a relatively small effect on the ultimate strength at the effective cross-section. On the other hand, the results of component tests indicate that the cyclic deformation capacity of both double-angle and Z-shaped double-angle brace is much lower than that of the single-angle brace. In the case of L65x6 cross-section, a cumulative plastic ductility ratio of both double-angle and Z-shaped double-angle brace is decrease to roughly 5% to 20% of the single-angle brace. Conclusively, although the removal of the out-of-plane eccentricity brings the increase in the connection strength of angle brace, it causes the decrease of the cyclic deformation capacity as the whole member.
A buckling-restrained brace is an excellent structural member. In medium- and low-rise buildings, it is often used primarily as an earthquake-resistant brace, and in super-high-rise and high-rise buildings, as a seismic-response controlled brace1-3). It is particularly important to assess the fatigue performance of a buckling-restrained brace where it is used as a seismic-response controlled brace. This study summarizes the results of two studies performed on a buckling-restrained brace using steel mortar planks10,12). A fatigue test using constant strain-amplitude cyclic loading was also conducted under the following two conditions: 1) Using large plastic strain-amplitudes of axial strain exceeding 3% assumed in massive earthquakes, 2) Decreasing the value of restraining index R that affects energy dissipation performance. By combining the results of the test and past studies, the study constructed a fatigue curve in the plastic region. Based on the fatigue curve, a detailed examination was conducted on the tolerable loading cycles Nt, locations of fracture and local deformation, cumulative plastic strain energy ratio ω, compressive-to-tensile strength ratio α and restraining index R for both basic type and high-performance type specimens. Focusing on the buckling-restrained brace using steel mortar planks, a constant strain-amplitude cyclic loading test was conducted using basic type and high-performance type specimens. The following results were obtained: 1) In both types of specimen, strain-amplitude ε and tolerable loading cycles Nt in the plastic region have a linear relationship when plotted on a double logarithmic graph, from which the fatigue performance of the buckling-restrained brace can be estimated. 2) In both types of specimen, at high strain-amplitudes of axial strain exceeding 3%, the fatigue performance of the brace is determined by the fatigue performance of its core plate, hence, there is little difference in tolerable loading cycles Nt and cumulative plastic strain energy ratio ω between the two types of specimen. 3) In both types of specimen, at small strain-amplitudes of axial strain less than 3%, the fatigue performance of the brace is determined by the shape of the stress concentration location: a weld heat-affected zone in the case of the basic type specimen, and the end part (R part) where the area of the core plate plastic zone is decreased in the case of the high-performance type specimen. The high-performance type specimen is superior in both tolerable loading cycles Nt and cumulative plastic strain energy ratio ω. 4) Even for the high-performance type specimen which has a better performance than the basic type specimen, compared with the fatigue performance of the steel material, tolerable loading cycles Nt is 1 / 5.7 times with a strain-amplitude of 3.0% and 1 / 3.5 times with a strain-amplitude of 0.3%, which is a small number of times. 5) Tolerable loading cycles Nt of the basic type specimen was 5 at a strain-amplitude of 4.0%, while that of the high-performance type specimen was 2 at a strain-amplitude of 5.5%, 3 at 4.5% and 5 at 4.0%, demonstrating sufficient performance to withstand large strain-amplitudes. 6) In both types of specimen, the cumulative plastic strain energy ratio ω at a strain-amplitude of 3.0% or less greatly exceeded the values derived from the performance evaluation formula proposed in the past study11), demonstrating adequate energy dissipation performance. 7) As our past studies showed, in both types of specimen, as strain-amplitude ε increases, compressive-to-tensile strength ratio α increases.
Steel products which have various characteristic (e.g. high ductility, high yield stress, low yield stress and high weldability) are used as main structure of building by diversification of demanded application, and technology for steel manufacturing has developed. Because steel square tubular member is processed cold-forming and welding in the process of manufacturing, residual stress will exist in the products. Moreover, due to the cold-forming process geometrical initial imperfection, i.e., global and local, will exist. These initial imperfections are still remained even so the technology for steel manufacturing is developed. The influence of the initial imperfection on the performance of the column is well known. However, the effect of the initial imperfection on the elasto-plastic behavior of square steel tubular columns under compressive axial force with one end bending moment is not clarified. In this paper, firstly, the effect of initial imperfection (i.e., initial global imperfection, initial local imperfection or residual stress) on the elasto-plastic performance is investigated independently; comparison between the experimental results are shown. Secondly, the effect of composite initial imperfections on the elasto-plastic performance is investigated. Firstly, followings were found from the analysis results where initial imperfection is introduced in the member individually. 1) The amplitude of the global imperfection has an impact on performance of the column. Also, the direction of the global imperfection has an impact on performance of the column. When the ultimate behavior was determined by local buckling, the deformation capacity decreased with an increase the amplitude of global imperfection to windward. On the other hand, when the ultimate behavior was determined by bending deformation in in-plate, the deformation capacity increased with an increase the amplitude of global imperfection. 2) The amplitude of the local imperfection has a great impact on performance of the column. The maximum bending moment and the deformation capacity significantly decreased with an increase the amplitude of local imperfection. 3) The magnitude of the residual stress which changes in plate thickness direction hardly has an impact on performance of the column. However, the amplitude of the residual stress which does not change in plate thickness direction has an impact on performance of the column. Secondly, followings were found from the analysis results where composite initial imperfections are introduced in the member. 4) The amplitude of the local imperfection is the most influential initial imperfection on the deformation capacity of the column, and the deformation capacity decreased with an increase of the amplitude of local imperfection. The influence of the amplitude of the global imperfection is insignificant on the deformation capacity. On the other hand, the amplitude of the global and local imperfection and the magnitude of the residual stress do not have significant impact on the maximum bending moment. 5) Validation of the numerical simulation were also performed; initial imperfections that can simulate test results in reasonable accuracy was shown.
Steel and concrete are commonly used as construction materials for building structures. The force transfer mechanism in the connections between steel and concrete includes friction, bearing, bonding and mechanical shear connecting. This force transfer mechanism was summarized in the AIJ Design Standard for Composite Structures in 2014. The force transfer mechanism of connections of composite structures comprises the mechanism of shear force causing relative slip along the contact surfaces between steel such as steel plate and concrete and is due to the effect of friction and bonding, which is the fundamental properties of the force transfer mechanism between steel and concrete. It is important to quantitatively evaluate the force transfer mechanism s performance due to friction stress and bond stress and to accurately incorporate it into a method for evaluating the strength of connections in actual building structures. On the other hand, reproducing the experimental results of the shear connector using perfobond strip requires to consider frictional and bonding resistance between steel and concrete, as well as the direct shear resistance of concrete across the opening in perforated steel plate. Similarly, in experiments on connections with headed studs, the contact surface between the steel plate joined to the stud and the concrete also needs to be evaluated. In this paper, ultimate and residual stresses under restriction stresses applied perpendicularly to the contact surface for friction and the bonding behavior of the contact surface between steel and concrete is investigated by conducting push-out tests mainly on specimens using high strength concrete and high restriction stress. It is clear from a database including these and previous test results that the ultimate and the residual stresses are linearly proportional to the restriction stress irrespective of the contact surface condition. Furthermore, this paper proposes new formulations for ultimate and residual stresses under restriction stress to the contact surface on friction and bonding behavior of contact surfaces between steel and concrete. Predictions from the proposed formulation agree closely with test results under various contact surface conditions.
In this study, creep tests for cast-in-place anchor, inorganic-type post-installed bonded anchor and organic-type post-installed bonded anchor were conducted using deformed bar D13. The inorganic-type anchor contained ultra-rapid hardening cement, sand, and other materials in a cartridge. As for the construction procedure, water was poured into the top of the cartridge. After that the materials were mixed using a special mixer in the cartridge. They were then injected into a drilled hole with a caulk gun. The main component of the organic-type anchor is an epoxy acrylate resin. The organic-type anchor is formed by mixing a base agent and a hardening agent in a mixing nozzle, the resin filled in the drilled holes. The concrete was placed in steel pipes to prevent splitting failure. The steel pipe had an outer diameter of 216 mm and a thickness of 4.5 mm. D13 was used for the anchors. The embedment length was seven times the nominal diameter of the deformed bar. The bond strength tests were performed in more than one month after the anchor was fixed. In the creep test, a specimen was placed in the upper part of the apparatus, and a sustained load was applied with a coil spring. The bolt in the lower part of the apparatus was tightened after the spring was compressed with the hydraulic jack. The specimen was then subjected to sustained loading when the load applied by the hydraulic jack was removed. The tests were conducted at 20 °C and 60% relative humidity. The displacements were measured every 5 kN to reach the sustained load. The steel plate was positioned similar to the bond strength test. One-third of the ultimate load was first applied and removed. The procedure was repeated thrice after that. The sustained load was applied at the target load level. The sustained loads, which were 0.26-0.95 times of the ultimate load, were applied in over three months to evaluate the influence of the sustained load. For the inorganic-type anchor, creep characteristics were evaluated in accordance with EOTA ETAG 001 Part5. The evaluation results from the free end are different from them from the loading end. If the displacement at ultimate load is small, the variations in specimens and the error of estimation formula are considered to affect to the estimated time to creep failure. Creep deformation amount of long-term from the creep curve has been estimated by the exponential and logarithmic functions. In loading period 50 years, the value estimated by an exponential function is 1.5 times larger than the value estimated by the logarithmic function. The slope of the estimated equation from the creep failure and the creep curve has become equal by applying a logarithmic function to the inorganic anchors. Creep exponent of post-installed anchors from Norton law is approximately 3 at 20 °C.
Reinforced concrete columns formed with high-strength concrete have been developed for use as axial force carrying members. They have a reduced cross section compared with conventional “short” columns and are known as “slender” columns. These columns realize larger building interior spaces and offer architectural space with good visibility. However, under fire conditions, bending stiffness of RC columns decreases considerably due to thermal degradation of the cover concrete. It is anticipated that slender RC columns would be more vulnerable to buckling failure than to cross sectional failure. The authors have proposed an evaluation method based on tangent modulus theory for the buckling strength of straight RC columns subjected to centric axial load in fire, and shown that this proposed method offered a good approximation of both experimental fire-resistance time and failure mode. However, existing members have initial deformation formed in manufacturing process. For this reason, it is anticipated that slender RC columns with initial deformation fails earlier than straight ones. This paper presents the main results from an analytical study of slender RC columns with initial deformation shaped sine wave under fire conditions, leading to a discussion of fire performance, which includes deformation behavior and fire-resistance time. All analytical models consist of concrete with a compressive strength of approximately 120N/mm2 and have a square section where the length of one side is 250mm and 5000mm in height. From thermal stress analysis in consideration of geometrical nonlinearity, the followings are obtained: 1. Fire-resistance time of slender RC columns whose the initial deformation α/h was less than approximately 1/103 decreased sharply. 2. There are two failure modes of slender RC columns with initial deformation which are buckling and three-hinged mode. 3. The time, while columns resist an axial force after they start to bend at the time evaluated by the analytical method based on tangent modulus theory, is approximately 10~15 minutes. 4. The larger transient strain was, the shorter fire-resistance time was because the large additional moment occurred with bending deformation increases in fire. 5. The directions of initial deformation have little influence on fire-resistance time. 6. The mechanical boundary conditions at edge of columns have large impact on fire-resistance time.