The purpose of this study is to investigate the actual condition of concrete carbonation according to each direction for existing RC buildings covered with finishing mortar as a finishing material for the exterior to evaluate its effectiveness suppressing carbonation for each direction. There are some previous studies that report on the difference in progression of carbonation according to each direction for exposed concrete sections of existing buildings. However, there are few studies that report on cases or conduct a detailed analysis on the factors regarding the progression of carbonation by each direction for concrete covered with exterior finishing material.
In general, the surfaces of buildings are covered with external finishing materials, so it is rational and crucial to consider the effect of the finishing materials suppressing carbonation when evaluating the progression of carbonation in concrete. Also, when conducting a durability study on an existing RC building, there is a limited scope of the building where investigation is possible in many cases. Therefore, having a grasp on the degree of impact that a difference in direction tends to have on the progression of carbonation as numerical data is beneficial in that one can appropriately estimate the entire condition of the building from the survey results of one portion.
Research was conducted for this study following the process below. First, for 100 collective residential buildings, 200 core samples were collected from the north and south sides of structural concrete wall. The depth of carbonation, the thickness of the finishing mortar and other factors was measured, to investigate the difference in carbonation of the concrete according to each direction. Next, the above data were applied to a formula that replaces the carbonation suppression effect from the exterior finishing material with the depth at which carbonation is delayed, thus deriving the carbonation resistance of finishing mortar and the carbonation rate by each direction. Furthermore, we considered the trend of carbonation from the perspective of difference in environmental factors due to direction or, in other words, the difference in temperature and relative humidity.
The results are as follows. The average carbonation resistance of the finishing mortar was 3.83 √years for south-facing walls, 5.13 √years for the external side of north-facing walls and 5.00 √years for the internal side of north-facing walls. The average carbonation rate of the finishing mortar was 7.69 mm / √year on south-facing walls, 4.95 mm / √year on the external side of north-facing-walls and 4.98 mm / √year for the internal side of north-facing walls. The average ratio of carbonation rate of the finishing mortar between the north-facing and south-facing wall of the same building was about 1.62.
In this study, combined deterioration mechanism in reinforced concrete with CO2, flying salt, acid rain is reconstituted by transient reaction-diffusion equation and super long-term deterioration process is analyzed in RCP scenario.
This method is confirmed to be consistent with research of the past about carbonation and to be suitable for complex hysteresis in RCP scenario.
Simple formula for building group is also formed and reliability design method with mixture distribution of carbonation in several RCP scenarios is proposed. Probability of carbonation by mixture distribution increases in durable member with thick cover depth after 100 years.
As the prerequisite definition in our research, “no-shoes-floor” is the floors that person takes off his shoes. In Japan, popularly, we live at dwelling houses and elderly facilities without shoes. “No-shoes-floor” life-style can be made a lot of behavior, such as walking, sitting, lying, etc. Therefore, body regions that touch to floor surface, or motions against floor have more complex and more multifarious than western style living. The final goal of our research is the establishment of evaluation methods of floor deformation properties considering comfortableness human behavior. In previous paper, we constructed the psychological scales by the sensory tests about comfortableness of various activities. In these activities, we only focused on an establishment of evaluation method for walking. At the next step, in this paper, we establish an evaluation method of touching body regions under multiple human activities. At preliminary experiments, we guess that local deformations on floors have much relation for evaluation of these activities. Under result of preliminary experiments, we need to measure deformation behavior at both of loading point and surrounding areas for establishment of evaluation method. At second, as the reference from the mutual relationships of psychological scales in previous paper, we guess that it is not need to replace loading condition of one activity when the deformation behavior is measured. In addition, we guess that it is not need to measure the deformation behavior by dynamic loading condition at each experiment. Based on the above reasoning, static loading device was developed by altering dynamic discrimination device which is for evaluation method for walking in previous paper. We measured deformation behavior at loading point and surrounding areas, and examined relationships between the deformation and psychological scales. As a result, DC shown below was established as performance value which is corresponding to psychological scales. DC = 40D0 - 40D40 40D0: amount of deformation at the loading point while loading 40kgf 40D40: amount of deformation at 40mm distance from the loading point while loading 40kgf Finally, we established following method as evaluation method of deformation properties of no-shoes-floor for activities touching body regions except soles with floors. 1) The deformation behavior is measured by using static loading device. 2) DC is calculated from the measurement result. 3) DC is collated with the relationship figures between DC and psychological scales in this paper. In summary, the evaluation methods of no-shoes-floor deformation properties which human behave various activities on are following. 1) The performance values are calculated from the measurement result of deformation behavior by using dynamic discrimination device as shown in previous paper. 2) DC as the performance value is calculated from the measurement result of deformation behavior by using static loading device as shown in this paper. 3) The above performance values are collated with the evaluation indices shown in these papers.
After Parkfield earthquake in 1966 and San Fernando earthquake in 1971, various aspects of near-fault ground motions have been clarified and the effect of near-fault ground motions on structural response have been investigated extensively. The fling-step and forward-directivity inputs have been characterized by two or three sinusoidal wavelets. For this class of ground motions, many sophisticated analyses have been conducted from various viewpoints. However, as far as a forced input is employed, both a free-vibration term and a forced-vibration term appear and the closed-form expression of the elastic-plastic response may be difficult. In order to overcome this difficulty, the double impulse has been introduced as a good substitute of the near-fault ground motion and the closed-form expression of the undamped elastic-plastic response of a structure under the critical double impulse has been derived in the previous works. In this paper, the double impulse is introduced again and the closed-form solution of the maximum deformation of the elastic-perfectly plastic single-degree-of-freedom (SDOF) system with viscous damping under the ‘critical double impulse’ is derived. Because only the free-vibration appears after each impulse of such double impulse, the energy approach plays an important role in the derivation of the closed-form solution of the maximum elastic-plastic response of the SDOF system with viscous damping. However, it is difficult to treat exactly both of hysteretic damping and viscous damping even in the theory using double impulse. The quadratic-function approximation for the damping force-deformation relationship and the assumption that the critical timing of the second impulse is characterized by the stage of the zero restoring force after the first impulse are introduced to derive the maximum elastic-plastic response with viscous damping by using the energy balance formulation. The validity of the proposed theory using the quadratic-function approximation and the assumption of the critical impulse timing has been investigated through the comparison with the critical elastic-plastic response under double impulse using the time history response analysis. The validity of the proposed closed-form solution has also been demonstrated through the comparison with the response analysis to the corresponding one-cycle sinusoidal input as a representative of the fling-step near-fault ground motion. Furthermore, in order to investigate the applicability of the proposed theory to actual recorded ground motions, two recorded ground motions have been taken into account. It has been demonstrated that the maximum response to the critical double impulse and the response to the selected ground motion coincide fairly well. This supports the validity of the proposed theory.
Damage to foundation structures which cause inclination/settlement of buildings resulting in prohibition of the usage has been reported after recent earthquakes in Japan. Such damage was often observed to boundaries between superstructure and foundation structure with piles. In order to make judgement of availability of earthquake-damaged buildings with pile foundation, assessment of piles is indispensable; however, there are very few experimental researches clarifying the behavior of column-foundation beam-pile joints which are subjected to complicated seismic loads. Therefore, a series of experimental tests for the column, foundation beam and cast-in-place pile joints under realistic seismic loads was conducted to obtain the fundamental data, which is likely to provide key behavior to detect damage to the pile foundations after seismic events. In this study, a SRC building damaged to the foundation beams, piles, and pile caps in the 1995 Kobe earthquake was focused (Figs. 1 to 3). In particular, an exterior column-foundation beam-pile joint with severe damage was targeted. Shear forces applied to the exterior pile are affected by complicated seismic actions, namely, inertial forces at the foundation slab and beam as well as shear and variable axial forces to the exterior column. Therefore, numerical analyses using several models considering superstructure-pile interactions (Fig. 4, Tables1-4) were conducted to evaluate the seismic loads applied to the target joint. As a result, the inertial force at foundation was approximately 0.5 times the column shear force (Figs. 5 to 8). Based on the analytical findings, an experimental method for exterior column-foundation beam-pile joints simulating the realistic seismic behavior was proposed and applied to the structural tests. Four 1/3-scale specimens were prepared considering two parameters which were the existence of a superstructure wall on the foundation beam and the volume of the pilecap (Figs. 9-10, Tables5-7). The specimens were supported with a pin at the inflection points of the column and pile, respectively, and a roller at that of the beam. Horizontal cyclic loads were applied to the ends of column and foundation beam with a ratio of 1:0.5 simulating realistic shear distributions to the column and pile (Figs. 11-12). Variable axial loading was also applied to the column (pile) proportional to the applied shear force. In the cases of the specimens without the wall, the stiffness significantly decreased with flexural yielding at the end of foundation beam and the top of pile during the loading cycle to 0.5 ×10-2rad in the positive and negative directions, respectively (Fig. 13). On the other hands, in the cases of the specimens with the wall, the strengths rapidly dropped by concrete crushing at the top of pile during the loading cycle to 1.5 ×10-2rad. In particular, shear cracks on the pilecap were observed in the specimen with smaller pilecap representing the target building; however, the damage was less severe than that observed in the building. Typical bending analyses considering the post-peak strength deterioration for concrete well simulated the test results (Figs. 14-15). Furthermore, strain decreases of the beam longitudinal rebar were observed with the concrete of pile crushing (Fig. 16), which may provide a scheme to detect damage to pile foundations. Consequently, the fundamental behavior/performance of the exterior column-foundation beam-pile joints were experimental evaluated, which contributes to assess damage to piles as well as to improve the seismic design.
To obtain ultimate characteristics under various loading conditions for 1600mm diameter of large scale lead rubber bearing (LRB) which was designed as a seismic isolation device for nuclear power facilities in Japan, a series of break tests (i.e. horizontal loading break test under various vertical pressure and tensile loading test under various offset shear strain) were planned and performed as a part of the project “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities” of Ministry of Economy, Trade and Industry. Because of determination of the safety margin of seismic isolated structures against beyond design earthquake ground motion level, ultimate characteristics of isolators should be evaluated. As a result of those tests, some new knowledge was obtained. For example, while vertical pressure dependence for break shear strain is small, however offset shear strain dependence for break tensile strain is large and its dependence is non-linear. In this paper, for the purpose of clarifying the non-linearity of offset shear strain dependence for break tensile strain, new analysis method which can predict a break tensile strain under various offset shear strain was examined. Generally, in the case of predicting break strain, break criteria and its threshold value must be defined. In this study, we proposed the break criteria and its limit value for LRB. As a result, we could find stretch ratio λ1 as a one representation of break criteria. By taking the criteria, we clarified the reason of non-linearity of offset shear dependence for break tensile strain and performed parameter study by using proposed analysis method for the purpose of examining various parameters dependence (i.e. stiffness variability of LRB, break strain variability of rubber and lead plug diameter). In addition, we proposed two other break criteria. One is linear sum of maximum principal stretch ration λ1 and minimum principal stretch ratio λ3 and the other is strain energy density function. Construction of this paper is as follows; In chapter 1, outline of this study is explained. In chapter 2, outline of proposed analysis model is explained. In chapter 3, validity of analysis model is shown by comparing test results. In chapter 4, using proposed analysis model, analytical prediction method based on FEA is proposed and analysis of break test result is performed. In chapter 5, based on proposed analytical prediction method, various parameter dependences for break characteristics of LRB were examined. In chapter 6, probability of other break criteria is considered. In chapter 7, conclusions of this study are described.
The damaged mud walls and inclined columns are found commonly in very old houses such as traditional wooden houses. In case of the seismic strengthening works of these houses, however, the inclined columns are often not restored because of a higher cost and wall clay are applied to the damaged mud wall with inclined columns. In such cases, it is not clear about the failure mode and P-Δ effect on the strength. In the present study, in-plane shear tests were performed on mud walls with inclined columns, and the failure mode and P-Δ effect on the strength are verified. In addition, numerical computation with 3D frame model of the houses was conducted in order to verify the effect of the inclined columns on the seismic strength of the houses in the large deformation area. The configuration of the specimen is shown in Fig. 1, and the parameter of specimens are given in Table2. Specimens 1-1 and 1-2 are the standard specimens with normal frame and Specimens 2 and 3 are the specimens with inclined columns. The ultimate deformation states of Specimens 1-2 and 3 are shown in Photo3 and Fig. 3. In all specimens, the cracks were observed along the penetrating beams called Nuki in 1/100 rad and a part of wall clay was taken off in 1/50 rad. As the results, there was no significant differences in failure mode among the specimens. The relationship between the load and drift angle is shown in Figures 4 and 5. In Specimens 2 and 3 with inclined columns, the load decreased rapidly as the drift angle increased because of the negative shear force due to the P-Δ effect. In addition, the inclined columns were found to be sunk into the base by cyclic loading (see Fig. 7) because of the stress concentration, verified by 3D FEM Analysis using LS-DYNA, a general-purpose FEM analysis program (see Fig. 10). The analytical model of a one-story house is shown in Fig. 19. A total of 2 models, Model -1 is the house with no inclined columns and Model -2 is the house with inclined columns, are constructed. The detail of the analytical model of seismic walls is shown in Fig. 15. The model is separated into 2 parts, one is the column-beam frame with mud walls which is taking account of the shear force and the bending deformation of the joint between column and beam, and the other is the rigid frame which is taking account of the P-Δ effect. Wallstat, which is the collapsing simulation program for wooden structures based on the Distinct Element Method, is used for the analysis because the P-Δ effect can be considered in this program, and the deformation incremental analysis is conducted. The analytical result, which is the relationship between the story shear force and drift angle, is shown in Fig. 20. The story shear force of Model -2, considering the inclined columns, decreased compared to that of Model -1 because of the P-Δ effect and the decreased ability of the joint between column and beam.
Shear walls deform not only in in-plane direction but also in out-of-plane direction by earthquake ground motions. Little experimental data of structural wall failing in shear are available on the influence of out-of-plane deformation on in-plane seismic resistance. Structural performance of shear walls such as load carrying capacity and deformability has not yet fully been investigated when they deform in its out-of-plane direction along with in-plane direction. Shear capacity reduction by bi-directional loading is expected, but in practical design it is not taken into account. The objective of this study is to investigate the influence of out-of-plane deformation on in-plane shear resistance of wall failing in shear. The paper reports bi-directional cyclic loading tests carried out by the authors. The test results will contribute to establishment of design methods.
Three 1/3-scale reinforced concrete shear walls were constructed. The specimens were composed of a wall panel and two boundary columns. Their cross sections and reinforcement arrangement were the same in all the specimens. They were designed to fail in shear prior to flexural yielding in in-plane direction, and to fail in flexure in out-of-plane direction prior to shear failure. They were tested under bi-directional cyclic lateral loading simulating earthquake ground motions and the vertical load 840kN was also applied as service load. The test variable was the ratio of out-of-plane to in-plane deformations, which was 0, 1.5 or 3.
Out-of-plane deformation caused flexure cracks in wall panels and concrete crashing by compression at the corner of the boundary columns. All the specimens reached their maximum load carrying capacity at the inter-story drift of 0.5% or 0.75%. The maximum lateral loads of the specimens subjected to bi-directional loading were approximately 8-18% less than that of the specimen subjected to uni-directional loading. Shear deformation was about 80% of the total in-plane horizontal deformation in all the specimens.
An estimation method for shear capacity of shear walls under bi-directional loading was proposed. The interaction between lateral load capacities in the in-plane and the out-of-plane directions takes the form of two concentric ellipses. One is an ellipse denoting flexural yielding and the other is the one for shear failure. The maximum load resistances of walls subjected to bi-directional loading are schematically shown as the inscribed curve bounded by the two ellipses.
Experimental studies to examine the effects of opening on flexural strength and ultimate deformation using reinforced concrete column
specimens with a holed sidewall failing in flexure were reported. The target of this test series was to get the limitation on location of
openings to avoid their effects. In other words the locations of openings were examined so that holed sidewalls show the same flexural
performance as un-holed sidewalls. Eight specimens were tested. Seven of them were specimens with one holed side wall. Main variables
were the location of openings. Using these test results the proposed limitation lines on location of openings to avoid their effects for
flexure was found to be effective for practical design.
Recommendation for Limit State Design of Steel Structure (LSD) specifies the requirements for columns to guarantee sufficient strength and ductility.
However, the requirements stipulated in LSD are based on the monotonic test results that were conducted by H-shaped steel columns. It is necessary
to confirm the elasto-plastic behavior of square steel tubular column under compressive axial force with cyclic bending moment. Also, it is important
to compare the monotonic test results and the cyclic test results. In this study, testing where axial force with one end cyclic bending moment are
applied to the column simultaneously are conducted. Moment capacity, deformation capacity and the second-order effects that will be caused by Pδ
moment were evaluated from test results. Comparison with LSD requirements and comparison with monotonic test results were also shown.
Cold-formed steel members are widely applied in columns and other axial members in steel structures. One of the key issues in design of cold formed steel is local buckling strength under axial compression. As a means to avoid premature local buckling, we have paid on attention to the application of octagonal section members. The local buckling behavior of octagonal section members have been investigated by many researchers. However, these studies have focused mainly on regular octagonal sections and do not considered the restraining effect between adjacent plate elements. In this paper, we conducted numerical analysis (Finite Strip Analysis and Finite Element Analysis) and stab column tests, to investigate the elastic buckling strength and post buckling strength of octagonal section members where the adjacent plate elements have different width-thickness ratios. First, we conducted Finite Strip Analysis to investigate the elastic buckling strength of octagonal section members. Through these numerical analysis, it was found that the octagonal section members generally showed higher strength than that of simply supported plate. These strength increases were depended on the difference of the width-thickness ratio between adjacent plate elements and the change of buckling mode. Second, we examined the post buckling strength of octagonal section members through a stab-column compression test. We compared the post buckling strength of square section and that of octagonal section, and found that the post buckling strengths of octagonal section members was higher than those of square section members, when they have a same diameter. In addition, it was known that the post buckling strength of octagonal section members could be evaluated by the traditional effective-width method, where simply supported conditions were assumed. Finally, we investigated the post buckling strength of each plate elements of octagonal section members whose adjacent plate elements have different widths by Finite Element Analysis. The post buckling strength of the plate elements with a large width was higher than of square section member. On the other hand, the post buckling strength of the plate elements with a small width was lower than that of square section member. These increase and decrease were dependent on the restraining effect between adjacent plate elements. Because of this trade-off effect between the adjacent plate elements, the effective width method, which regarded each plate elements as a simply supported plate, gave a good estimation about post buckling strength of the octagonal section members.
Web-tapered tapered H-shaped beams, which have a continuous reduction in section, have been utilized in steel-frame structures for more efficient utilization of structural materials. On the other hand, section stiffness decreases along a beam's axis, and the member stress increases. For this reason, it is more important to investigate the buckling behavior and the progress of the plasticity of a tapered H-shaped beam than that of a uniform H-shaped beam. In the past, the authors investigated elastic plate buckling strength and lateral torsional buckling strength using an energy method and numerical analysis. An estimation method and formula were proposed in those research studies. This study examines the inelastic buckling strength and plastic deformation capacity of Web-tapered H-shaped beams with depth tapered through by a cyclic loading test and numerical analysis. Twelve tapered beams and five normal straight beams were tested. The cyclic behavior and collapse mode of these specimens were investigated. In addition, multiple simulations using numerical analyses were carried out. Then, the collapse mode and plastic deformation capacity of the tapered beam were evaluated by using indexes that were determined on the basis of the elastic buckling strength. First, it is clear that the behavior and collapse mode of tapered beams are changed by the following characteristics: taper gradient, flange plate slenderness, web plate slenderness, and lateral bracing length. The skeleton curves of each specimen are taken from the load-displacement relationships obtained by a cyclic loading test. Using these skeleton curves, the effects of a tapered gradient on the performance of an H-section beam are examined. The value of the plastic deformation capacities of beams collapsed by web plate buckling or lateral torsional buckling are estimated from the eigenvalue of each tapered beam. This means that the plastic deformation capacity increases when the eigenvalue is higher. On the other hand, the values of the plastic deformation capacity of a beam collapsed by flange plate buckling are almost the same without regard to its own eigenvalue. Because the flange plate buckling strength decreases when the tapered gradient is steep, and plastic reason in flange is longer. Second, the effect of a cyclic load on tapered beams is considered. It is evident that beams with low plate slenderness and large plastic deformation capacity are affected by cyclic loads. That value The plastic deformation capacity of these beams decreases by cyclic loading. Third, the authors propose a new plate buckling slenderness index (WFγ) and lateral buckling slenderness index (γb). These slenderness indexes are obtained from the elastic buckling strength. It is clear that the collapse mode of a tapered beam can be classified using these indexes. In the range of WFγ / γb > 2.4, the collapse mode is plate local buckling, and in the range of WFγ / γb < 2.4, the collapse mode is lateral torsional buckling. Finally, the maximum strengths and plastic deformation capacities of tapered beams are estimated by using the plate buckling slenderness index and lateral buckling slenderness index when the collapse mode of tapered beams is classified by these indexes. The elastic buckling strength of the tapered beams do not decrease as a result of the coupled instability effect between the plate local buckling and lateral torsional buckling. However, the maximum strength and the plastic deformation capacity decrease as a result of these effects.
From lessons of the 2011 Tohoku earthquake and other earthquakes, it becomes clear that the quick procurement of an emergency public shelter is very important to restore a function of a city. In the event of a disaster, structural engineers are required to estimate the seismic damage of structural components in buildings, and to judge whether these buildings are able to be immediately occupied or not as soon as possible. However, the visible damage can hardly be related to the damage of steel structural components directly, while crack width has been used as a clear damage index for RC structures. It is very important to establish a visible damage index for quick damage estimation of steel structures. In the previous papers, visible damage indices for exposed column base and an single brace with angle section have been established from the experimental studies. This paper focuses on the residual out-of-plane deformations in local buckling region of steel column to estimate its residual strength. In order to find the relation between the residual deformation and the out-of-plane deformation in local buckling region, cyclic loading tests of a steel column under axial compression force were carried out. The main parameter in these tests is the cross section of the column, which are cold-formed RHS-200x6 (depth x thickness), 200x9, 300x9, welded H-200x180x6x6 and H-200x200x6x9. In addition, the constant axial force which is 0.15 and 0.30 defined as the ratio to its yield axial strength is also selected as one of the parameters of the test. The major findings obtained from the test are summarized as follows: (1) the out-of-plane deformation in local buckling region was strongly related with the residual strength deteriorated due to the local buckling; (2) the out-of-plane deformation almost remained constant regardless of various residual story drift; (3) the rotation angle of column after deterioration is able to be converted to the out-of-plane deformation by a 3-hinge deformation model of the local buckling. Finally, from these results, the diagrams of the residual strength of steel columns based on the out-of-plane deformation in its local buckling region have been expressed as an example by using the Kato-Akiyama hysteresis model18),19).
The connection between a steel beam and a concrete slab in the composite beams of many buildings or bridges is generally manufactured with headed studs. In the revised Japanese Industrial Standards in 2011, headed studs of diameters of 10 mm and 25 mm were added. However, a consideration of their mechanical properties is not sufficient. The shear strength of headed studs is typically investigated via push-out tests; however, these tests are carried out under specific conditions, and the results of these tests are greatly affected by the test conditions. There have been only few studies on headed studs with diameters of 10 mm and 25 mm; however, there have been many studies on the mechanical properties of headed studs of other diameters, using push-out tests. Therefore, we collected test results on the shear strength that have been obtained from previous studies from other countries that performed push-out tests using headed studs. In this study, we define the subject of analysis, and attempted to discuss the tendency of shear strength comprehensively by investigating experimental data obtained through 1002 push-out test results. We divide it into failure mode and type of slab; we focus on the tendency of the shear strength from the test results. The shear strength of a headed stud in a solid slab was approximately equal to the product of the headed stud tensile strength and total cross-sectional area of the shaft component of the headed stud. The shear strength value is approximated because the results of the push-out test are influenced by the pure shear strength as well as the concrete strength. This tendency is especially prominent in case of failure of the headed stud. A similar tendency, although with variations, is observed in case of failure of concrete. The shear strength of a headed stud in a slab with a steel deck cut on the flange also shows a trend similar to the shear strength of a headed stud in a solid slab. On the other hand, the shear strength of a headed stud in a slab with a steel deck across the flange showed a different tendency. It is less than the shear strength of a headed stud in a solid slab. Although specimens having a slab with a steel deck across the flange can be classified into specimens having a headed stud welded through a steel deck and specimens having a headed stud welded to the flange directly, their shear strength tendency was almost equal. The shear strength of a headed stud with a diameter more than 25 mm in a solid slab gradually decreased with increasing diameter in both the failure modes. Through a regression analysis of the test results, we classified the results into three types. The first is the test result for a headed stud having a diameter less than 25 mm in a solid slab or slab with a steel deck cut on the flange. The second is the test result for a headed stud having a diameter of more than 25 mm in a solid slab. The third is the test result for a headed stud having a diameter of more than 25 mm with a steel deck across the flange; the test result for a headed stud having a diameter of more than 25 mm and welded through a steel deck is not included in the evaluation. Therefore, three expressions are listed in Table. 2 using the shear strength and total cross-sectional area of the shaft component of a headed stud and headed stud tensile strength.
1. Introduction The concrete filled steel tubular columns subjected to axial compressive force can be designed by using "Recommendations for Design and Construction of CFT Structures". Nowadays, as the strengths of materials are increasing and a wide variety of cross-section composition are observed in the actual structure, extension of the range of application is desired. The objective of this study is to propose the formulas for evaluating the ultimate or allowable compressive strength of CFT columns.
2. Strength of CFT Columns by the Current AIJ CFT Guide The current "Recommendations for Design and Construction of CFT Structures" is examined and the characteristics of the CFT Guide are described. The design formulas are shown in Eqs. (2)-(20). In the formulas, as the slenderness index, the buckling length to the section depth ratio is adopted. The strength of the concrete ranges from 18 to 90 N/mm2, and that of the steel tube ranges from 235 to 440 N/mm2. In this paper, the normalized slenderness ratio of a steel tube is adopted as the slenderness index, eliminating the categories of short, intermediate and slender columns, and the strength of concrete is allowed up to 150N/mm2.
3. Strength Estimation of Concrete Column and Steel Tubular Column The buckling strengths are calculated by superposing the strengths of concrete column and steel tubular column. At first the buckling loads of concrete columns are calculated by using the characteristic Equation (25), and approximate equations are presented as Eqs. (26)-(28). The buckling strengths of a steel tube are obtained by Eqs. (32)-(34) specified by the AIJ "Recommendations for Limit State Design of Steel Structures".
4. Proposed Strength The strength formulas are shown in Eqs. (47) and (51) for the ultimate and the allowable strength, respectively. For the circular short columns (normalized slenderness ratio sλ1<0.15), the confined effect can be considered as Eq. (50). In Figure 14, the proposed strengths are compared with those by the CFT guide. As shown in Figure 15, the value of (the current CFT Guide strength) /(proposed strength) ranges from 0.94-1.04 for square CFT columns and 0.94-1.15 for circular CFT columns. In Figures 16, 17 and 18 the experimental results are compared with the proposed strength. As shown in Table 3, the value of (experimental strength) / (proposed ultimate strength) ranges from 0.96-1.04 for square CFT columns and 0.97-1.15 for circular CFT columns. The proposed strength is in good agreement with the experimental maximum load.
5. Conclusions The conclusions derived from this study are as follows: 1) The formulas for evaluating the ultimate or the allowable compressive strength of CFT columns are presented as Eqs. (47), (50) and (51). 2) Strengths obtained by the proposed formulas are compared with those of current CFT guide, and it was shown that the value of the current CFT Guide strength/proposed strength ranges from 0.94-1.04 for square CFT columns and 0.94-1.15 for circular CFT columns. 3) Strengths obtained by the proposed formulas are compared with those of experimental results, and it is shown that the proposed strength is in good agreement with the experimental maximum load. 4) Proposed formulas are easy to use, because the categories of short columns, intermediate columns and slender columns are eliminated.
When a steel beam arranged in a steel frame is exposed to fire, compressive force, that is thermal stress, is generated in it with member temperature increase, because the liner thermal expansion is restricted by the adjacent members. It is, however, well known that the generated thermal stress is attenuated by plastic deformation occurred in the steel frame at elevated temperature, finally disappears when the heated beam exhibits collapse mode. The collapse temperature is independent of the thermal stress in case of stable plastic collapse mode. On the other hand, there is a possibility that the open cross-section beam unstiffened in the out-of-plane direction exhibits flexural-torsional buckling in the process of fire by acting the large compressive force. Since the flexural-torsional buckling resistance depends on the compressive force, it is considered that the member temperature at the flexural-torsional buckling depends on the thermal stress. The main purpose of this study is to clarify the flexural-torsional buckling behavior of the beam at the fire arranged in the steel frame and propose theoretical solutions on the flexural-torsional buckling temperature considering influence on the thermal stress. Three dimensional finite element analyses are conducted to verify the theoretical solutions. A line element being capable of analyzing the flexural-torsional behavior of the member is used. Both geometrical and material nonlinearity are considered in the numerical analysis. Three types of partial frame models including a fire compartment room are analyzed and their numerical flexural-torsional buckling and collapse temperatures are estimated, respectively. By comparison of the theoretical solution with the analytical results obtained by the parametric analyses, the following 1) and 2) were clarified. 1) The unstiffned beam at the fire exhibits the flexural-tosional buckling and the large buckling deformation in both in-plane and out-of-plane directions occurs with the temperature increase. The flexural-torsional buckling temperature becomes lower when the liner thermal expansion is strongly restricted by the adjacent members. However, the beam can sustain vertical loads after the buckling. The thermal stress is attenuated by the plastic deformation in both in-plane and out-of-plane directions generated in the buckled beam. The beam can resist up to the temperature when the thermal stress disappears. The collapse temperature is higher than the flexural-torsional buckling temperature, however, the plastic deformation in the out-of-plane direction is very large. 2) The flexural-torsional buckling temperature of the heated beam at the fire can be safely estimated by the theoretical solution proposed in this study. The collapse temperature of the beam after the buckling can be estimated by the theoretical collapse temperature based on the simple plastic theory. It is considered that fire resistance of the beam in the case when the plastic deformation in the out-of-plane direction cannot be allowed, for instance, in the case when the heated beam adjoins fire compartment walls, should be estimated by the theoretical flexural-torsional buckling temperature.
Large-scale natural disasters have caused a great deal of human and property damage in the past. In the 1995 Kobe earthquake, the greatest cause of death was building collapses that occurred in a wide area. Remote sensing technologies are quick and effective solutions for gathering information on significant and widespread building damage. Most of the techniques use a vertical shot, taken from a satellite or an airplane, and the building damage is extracted using image-processing technologies. However, in many cases, it is difficult to accurately analyze the damage to the middle and lower floors of the buildings with the existing structural analysis techniques that use only two-dimensional information such as photographs (taken vertically).
The SfM-MVS (Structure from Motion and Multi-view Stereo) technique can reproduce three-dimensional structures from the photographs taken at various angles from a variety of platforms. In this study, we applied this technology to aerial photographs of disaster sites due to the 2014 Hiroshima debris flow to validate the altitude accuracy of the developed three-dimensional models. In addition, we examined the relationship between the altitude accuracy and the spatial resolution of the images. Furthermore, we attempted to extract damaged buildings from the three-dimensional model of the disaster site due to the 1995 Kobe earthquake.
Comparing the three-dimensional models developed by the SfM-MVS for the affected areas of the Hiroshima debris flow and the DSM generated by LiDAR observation, the RMSE (Root Mean Square Error) of the difference value is 1.75 m in the whole observation area, 0.17 m in the mudslide area, and 1.38 m in the buildings. We found that the difference is large in the area with vegetation and around the outer perimeters of the buildings. By reducing the resolution of the aerial photographs, the altitude accuracy of the reconstructed three-dimensional models was evaluated to clarify the relationship between the spatial resolution of the image and the altitude accuracy. It is found that the altitude accuracy of a model in the whole observation area decreases as the spatial resolution of the input photographs is degraded. In the mudslide area, considerable variations were found in the difference values because the abrupt altitude changes caused by the outflow rocks and the rubble could not be coped with effectively.
This paper also performed the building damage extraction due to the 1995 Kobe earthquake based on the quantitative examination of the Hiroshima dataset. We used six aerial images taken at a vertical angle before the earthquake on May 8, 1994 and 30 photographs taken by a different institution after the earthquake on January 18 and 20, 1995. In addition, to understand the building exterior wall surface, still images were clipped from a video of the affected area, taken at an obliquely downward angle, from a helicopter. For extracting the building damage, for which visual interpretation is somewhat difficult due to altitude changes, the altitude difference of the building was calculated from the models constructed from the images taken with a vertical angle before and after the earthquake. The extraction ratio was about 80% and a high-accuracy extraction of damage was possible in both severe damage and no damage. In addition, even when the texture variation on the roof was small, the altitude change could be replicated well, as damage. Extraction errors were found to be more in the buildings with fewer reconstructed point groups and greater deflections. Finally, we reconstructed post-event three-dimensional model by adding oblique photographs taken from the helicopter in order to verify the altitude changes and damages of building exterior wall.