Most of the manufacturing industries have a certain amount of stock, i.e., material, unfinished product, finished product and so on, in various location in the production process. By this reason, even in production stop due to an earthquake, it is possible to supply products to the market by consuming the stock. On the other hand, for the reason that it is economically disadvantageous to have a stock, there is a necessity for a rational measure in deciding the amount of stock to be kept. Based on above-mentioned circumstances, the authors introduced stock in a production process, and evaluated effect of improving the recovery curve by stock consumption by means of probability theory in the previous paper (Matsumoto and Nakamura 2016). However, the study of required stock amount and simultaneous consumption of multiple stock have been left as a future study. In this paper, firstly we show the definition and evaluation method of the recovery curve and then propose a method that can be more simply evaluates recovery curve by decomposing a production process into series systems. Finally we propose a method that can consider the effect of the stock by applying stand-by redundant system. Amount of required stock in addition to the simultaneous consumption and priority in the case of the multiple stock in a production process are discussed. Furthermore, applicability of the proposed method is examined by example of a production process. Assuming a production process of a chemical plant which produces six products, amount of the stock consumption and improving effect to the recovery curve by stock were evaluated. The following results were obtained: · Stock can be modeled as a stand-by redundant system. · On series system, if the stock is inexhaustible, effect of stock is determined by the stock which located in the most downstream of the production process and does not depend on upstream-side-stock. · In the evaluation of the recovery curve, effect of stock is obtained by adding the stock consumption to the amount of production without stock. And the stock consumption is obtained by subtracting the amount of production without stock from that with stock. · If there are multiple stock in the series system, the upstream-side-stock consumption event is a subset of the downstream-side-stock consumption event. · By consuming the upstream-side-stock preferentially, balanced (It does not concentrate consumption to a particular stock) stock consumption can be achievable. The proposed method can be applied to the case that stock performs an important function such as water and gas supply system, water supply and drainage system of the building in addition to the manufacturing industry. Future study is to enhance the versatility of the proposed method. In addition, in this article, it does not mention the problems such as cost by having the stock and the damage correlation between components. Therefore, they are also a topic for future study.
When large-scale earthquake disasters occur, the damage tends to impact elderly people more significantly than younger people. Generally speaking, as people age, they become physically and mentally weaker, and their risk of death increases. The results of previous studies show that the death toll following earthquake disasters was influenced by age and gender of the population of a given disaster area, but that influence has not been quantitatively assessed. In this paper, we evaluate human damage as being a calculation formula based on the age structure of the population of a large-scale earthquake disaster area. We showed the death risk for each age group by quantitatively assessing the distribution of the death rate after having made disaster area population clear. The distribution of the dead is expressed as a formula, using age distribution based on past results. We examined the distributions of the dead for six earthquakes: the 1948 Fukui earthquake, the 1983 Central Sea of Japan earthquake, the 1993 earthquake off the southwest coast of Hokkaido, the 1995 Kobe earthquake, the 2004 Niigata earthquake, and the 2011 Great East Japan Earthquake. We found that the death toll correlates with age in cases of large-scale earthquakes, and the total expected death toll of future earthquakes was calculated using current population data. We applied this formula to the case of a hypothetical Tokyo inland quake. The death toll of a given earthquake varies according to the type and scale of the earthquake. Various factors influence how the death toll is determined. The formulae for predicting death toll based on either type or scale have been proposed by a couple of researchers so far. In this paper, we applied the death toll prediction formula proposed by Yutaka Ohta in 1983. The human damage data in the event of a large-scale earthquake disaster is provided as follows. (1) There is an obvious correlation between the age structure of the disaster area population and the death toll. The incidence rate of the dead represents the tendency of the death toll in each age group. (2) We precisely evaluated the death risk quantitatively, independently expressing the numbers in each age group. (3) The death risk differs depending on the type of quake. Two types of damage are expressed in the following formulas: Earthquake with heavy structural damage: αD=3.511×10-11X6-1.323×10-8X5+2.152×10-6X4-1.36×10-4X3+3.79×10-3X2-4.603×10-2X+0.741 Earthquake with heavy tsunami damage: αD=2.424×10-10X6-5.744×10-8X5+4.848×10-6X4-1.75×10-4X3+3.177×10-3X2-2.884×10-2X+0.4 (4) Based on our trial calculation of the potential death toll of a future Tokyo inland quake, it is necessary to consider changes to the age structure of the population in Tokyo.
Based upon the foregoing, considerations about old, unsafe houses built before 1981 (where elderly people generally live) are necessary to reduce the damage from a future Tokyo inland quake. It will be necessary to carry out detailed examinations focusing on the influence of earthquake death toll on age and gender using this formula.
During the 2011 off the Pacific Coast of Tohoku earthquake (the 3.11 main shock), Tokyo metropolitan area was suffered from long period ground motions with long duration generated from widely spread seismic fault rupture in east Japan Sea area. Indoor damages including slippage and overturning of huge furniture and cracks in wallpapers were reported in super high-rise RC buildings. In the metropolitan area, most of these buildings are constructed on soft deposit and supported by pile groups supported by engineering bedrock. Precise estimation of seismic response of piles is also required for the 3.11 main shock and future massive earthquakes, as well as damage estimation for upper structure. This paper describes dynamic behavior of a super high-rise RC building constructed in Tokyo area mainly focusing on seismic performance of pile group. The 3-D moment-resisting frame model including basement and pile group is constructed for the super high-rise residential building where seismometers are equipped at 3 floors. After the 3-D model is validated by comparison with observed records during the 3.11 main shock, pile stresses are evaluated along with nonlinear responses of the superstructure. Structural responses and pile stresses are also calculated for the 3.11 aftershock and future massive earthquakes focusing on whether the building has experienced the 3.11 main shock or not. Conclusions are summarized as follows; 1) The strong motion records during the 3.11 main shock observed at 3 floors of the target building are well simulated by the nonlinear response analyses for the 3-D moment-resisting frame model with piles by using records at pile tip level as the input motion. Pile stresses have not reached to yielding stress level during the 3.11 main shock. 2) Bending moments at pile heads under assumption of rigid foundation beams are larger than those for beams considering their flexibility. On the other hand, differences between two are smaller than those in the previous studies, because footing beam depth in the target super high-rise building is larger than that for low or middle-rise buildings. 3) The observed records during the 3.11 aftershock were well simulated by temporarily consecutive seismic response analyses after the 3.11 main shock, rather than independent analysis. Pile stresses during the 3.11 aftershock were also overestimated for temporarily independent seismic response analyses, because of the overestimation of upper structural responses resulting in increase of the inertial force applied at pile heads. 4) Structural response and pile stresses are estimated for the future scenario earthquakes, the Nankai Trough earthquake and the northern Tokyo Bay earthquake, focusing on experience of the 3.11 main shock. If the input level of the future earthquake is smaller or almost equal to that the 3.11 main shock, estimation of piles stresses could be different for experience of the 3.11 main shock due to difference of the inertial forces.
There are few study which focused on the fall of cargoes, while many automated warehouses shut down because of the fall of cargoes in past earthquakes. Here, the authors conducted experiments on them. These experimental studies were to investigate the slip of cargoes and the characteristics of vibration which is the main cause of the fall of cargoes. First of all, we examined the failures of cargoes on the upper part of the warehouse. As the results of the experiment, movements of cargoes were classified into four failure modes; slip mode, collapse mode, overturn mode, slip-collapse mixed mode. Above all, we focused on the slip mode. The reason is that other modes appeared for five or six layers, while it is impossible to stack these cargoes because of the corrugated carton strength which is provided by JIS and that the cargoes are encouraged to wrap with shrink. Second, we examined the movement of cargo slipping. It was assumed that the movement of cargoes and palettes were not the same, because of differences between the acceleration phases at top of cargoes and those of palettes. Moreover, coefficients of the friction were classified into static friction and dynamic friction, from the time difference between the rise of horizontal force and start of cargo slipping. Next, we showed the judgement method of the fall of cargoes (in the slip mode) and verified that the results of experiments can be explained with the displacement of cargoes and overturning moment of cargoes. Then we investigated the characteristics of the slip and the vibraiton of cargoes, which is the main causes of cargoes falling, especially for the slip mode. First, we showed that the vibration mode of cargoes assessed primary vibration mode by taking the displacement distribution of cargoes into consideration. For the slipping characteristics, the coefficients of friction were evaluated. The coefficient of static friction varied from 0.4～0.6 although we used the same palette. The coefficient of dynamic friction increases with the height of cargoes. For finding out the main factor that influence the volume of slip of cargoes in characteristics of input wave, we confirmed the relation between cargoes displacement and support beem acceleration as well as that between the cargoes displacement and support beem the velocity. The displacement of cargoes had the better relation with the support beem the velocity than the acceleration. For the vibration characteristics, we confirmed the relation between the maximum acceleration of palettes, the natural frequency and the damping coefficient calculated with system identification. The slip of cargoes and vibration characteristics which were the main causes of cargoes falling and associated coefficient of friction, natural frequency and damping coefficient, were evaluated experimentally. In the future, we will use the model which instructs the results presented in this paper, and investigate the effectiveness of the countermeasure to avoid the fall of cargoes. Moreover, we will verify the prediction method of cargoes falling using these results.
Recently, methods to obtain truss or frame with high stiffness by the topology optimization problem of minimizing compliance has been studied actively. In general, cross-sectional areas or shapes of each member are defined as design variables in such a topology optimization problem. Practically, since the member cross-sections are to be selected from predetermined candidates, the design variables are treated as discrete variables. Therefore, heuristics or mixed-integer programming (MIP) is selected as the algorithm for solving truss or frame topology optimization problems. In particular, MIP has an advantage that the global optimality of the solution is guaranteed mathematically. However, it is difficult for MIP to treat large scale problems because of the high computational cost. In previous studies, the topology optimization using MIP is limited to small-scale problems, such as trusses or 2D-frames. In recent years, second-order cone programming (SOCP) has attracted attention since it can be solved efficiently by using the interior-point method. It is reported in the latest study that mixed-integer second-order cone programming (MISOCP), i.e., the problem obtained by adding the integrity to some of the variables of SOCP, can deal with the large scale problem compared with MIP. In this paper, the topology optimization of 3D-frame, which is difficult to treat by using MIP, is solved by using MISOCP. First, the 3D-frame topology optimization problem of minimizing compliance is formulated as MISCOP by using the dual problem of total potential energy minimization problem. From this formula, various 3D-frame topology optimization problems of minimizing compliance in which various sets of cross-sectional shapes are defined as design variables are considered. In this paper, 3D-cantilever with tip load, latticed dome with central concentrated load, and simple building with vertical and horizontal loads are optimized by SOCP in various design value cases. In almost all of the optimization cases, the solver has terminated with finding the global optimal solution. In only a few optimization cases which could not find the global optimal solutions, the MISOCP solver was run with time limit and the best feasible solutions found by the solver are reported. These solutions are not necesarily global optimal solutions, but these are good solutions in the cases of this paper. As numerical experiments for comparison, topology optimization problems treated in this paper were tried to be solved by using MIP as well, but the optimal solutions could not be found at all within realistic computational time. The obtained main results are as follows: •The 3D-frame topology optimization problem of minimizing compliance can be formulated as MISOCP by using the dual problem of total potential energy minimization problem. •MISOCP can solve various large scale 3D-frame topology optimization problems which are difficult for MIP to treat because of the high computational cost. •For a larger problem which is beyond the capability of MISOCP, MISOCP cannot find the global optimal solution but can find solution good enough. The commercial solvers which treat MISOCP have been developed extensively, and calculation speed is improved year after year. Against this background, there exists a possibility that the MISOCP will become a powerful topology optimization tool for building structures.
Application of a seismic base-isolation system to nuclear power plants (NPPs) facilities using a 1600-mm diameter lead rubber bearings (LRBs) has been considered for the purpose of enhancing seismic safety. Obtaining the mechanical properties of the LRBs is important, especially over the design limit, so that the seismic safety margin of the seismic base-isolated structure can be estimated against seismic events beyond design basis. Recent studies reveal that the scaled effect appears on the ultimate properties of the rubber bearings at the axial tensile break. However, the ultimate properties of such a large scale LRBs have not been confirmed. Therefore, in this study, to evaluate the realistic mechanical properties of the full-scale LRBs design for nuclear facilities, break tests are conducted on real-size LRBs in order to avoid the difficulties considering size effect. This paper presents twenty-two break test results of the full-scale and half-scale LRBs, mainly focusing on two points: one is the mechanical properties of the 1600-mm diameter LRBs such as its basic properties, linearity limit properties, and ultimate properties and the other is the statistical model of the linearity limit and the break limit of the seismic isolator on the basis of the break test, which is applied to investigate the residual risk of seismically isolated NPPs. The break limit states of the full-scale LRBs are well-evaluated as expected; i.e., the breaking shear strains under the compressive stress exceed the commercial reference value of 400%. These results are consistent with the test results of the 800-mm diameter LRBs in this study and the previous test, it was suggest that the ultimate properties of the LRBs up to 1600-mm in diameter can be evaluated by the alternative 1/2 scale test. As a result from the break test at various loading conditions for the full-scale LRBs, the breaking shear strain in the shear break under the axial compression was found to be substantially constant regardless of the axial stress value. On the tensile break test, decreasing trend of the breaking axial strain with the horizontal offset amount increased has been confirmed. In detail, the decreasing trend of the breaking axial strain changes at the offset shear strain of 200%, the breaking axial strain of the large offset range is relatively smaller. From the deformed state of the LRBs on the tensile breaking, it was confirmed that axial deformation of the vicinity of the break initiation point located the upper and lower ends of the rubber layer is promoted by a bending moment caused by increasing horizontal offset amount and the axial tensile loading. A statistical model of the linearity limit and the break limit of the seismic isolator were evaluated on the basis of the break test of the full-scale LRBs. In accordance with the concept of the Japanese design guidelines for the seismically isolated NPPs, the regression formulas of the break limit were defined in the axial stress-shear strain plane, or the tensile strain-shear strain plane. Further, the regression formulas of the linearity limit were defined in the axial stress-shear strain plane. By using of these statistical model of limit state of the LRBs, a residual risk for seismic base-isolated NPPs against seismic events beyond design basis can be investigate more accurately.
This paper discusses the coefficient of effective wall-length of mud wall examined statistically using the data in cyclic loading tests reported in late years. The coefficient of effective wall-length is called “Kabe-bairitsu” in Japan. The Kabe-bairitsu of Japanese mud wall is 0.5 in the Enforcement Ordinance of the Building Standards Law. The mud wall fabricated by the specification in the notice No. 1543 of the Ministry of Land, Infrastructure and Transport in 2003 is the Kabe-bairitsu of 1.0 or 1.5. In many experiments of mud wall carried out recently, the numerical values of Kabe-bairitsu seem to be considerably high. Therefore the Kabe-bairitsu may be reevaluated. The 135 experimental data of mud wall is gathered in the paper published from 1990 to 2015. The mud wall taken here is plastered in both sides and the width of 1.8 meters. The experimental condition is not necessarily same. The plastering work has the regional characteristics. The place to dig clay is different. The specification of mud wall is various in the thickness of wall, the space distance of bamboo lathing and so on. The wooden frame of mud wall is various in the dimension of column, the dimension of Nuki, the connection method of column and sill, and so on. Moreover, there are three methods to prevent from being able to pull column up in the experiment. With disregard to these conditions, the average Kabe-bairitsu of 135 test data was 2.2 and the coefficient of variation was 0.25. The Kabe-bairitsu was not remarkably affected by the difference in each condition. The relationships between the Kabe-bairitsu of mud wall and the decision factors are investigated by scatter diagrams. There are four factors: (1) yield strength Py, (2) product of ultimate strength Pu by 0.2/Ds, where Ds is the structural characteristics factor, (3) product of maximum strength Pmax by 2/3, (4) strength of specific deformation P1/120 or P1/150. The factors (1) and (2) determined the Kabe-bairitsu in 95% of test specimens. The main observations from this statistical investigation on the 135 experimental data were as follows: 1. More than 95% of Kabe-bairitsu of 135 experimental mud walls were beyond 1.0. With disregard to the conditions of experiments and the specification of specimens, the average Kabe-bairitsu of 135 mud walls was 2.2 and the coefficient of variation was 0.25. 2. The coefficient of variation of Kabe-bairitsu evaluated by each condition or specification was almost less than 0.30. If the difference of condition and specification is disregarded and only the statistical dispersion of 0.061 in the 135 data is considered, the Kabe-bairitsu of 135 mud walls will be 2.4. When a reduction coefficient of 0.75 is adopted as the safety factor, the Kabe-bairitsu is 1.8. Also the confidence limit value of 95% in the Kabe-bairitsu of 135 was 2.1. When the reduction coefficient of 0.75 is multiplied by 2.1, the Kabe-bairitsu becomes 1.6. Even if the dispersion is considered, the Kabe-bairitsu seems to be more than 1.0 or 1.5. 3. The decision factor of the Kabe-bairitsu of mud wall was the yield strength Py or the product of ultimate strength Pu by 0.2/Ds. 4. The correlation between the horizontal rigidity and the Kabe-bairitsu of mud wall was relatively small. 5. The place to dig clay affected the Kabe-bairitsu of mud wall, but the influence of other variations in fabrication of mud walls was not so clear. 6. The mean of the structural characteristics factor Ds was 0.31, but the coefficient of variation was large relative to the other wooden load-bearing wall.
For the materials of the brace member in bearing walls of Japanese wooden houses, sawn lumber, laminted veneer lumber (hereinafter called "LVL") et al would be used commonly. Those members would be needed to resist compression and tensile force. Under the compression load, those member would be reduced the strength depending on the geometry. This phenomenon would be called buckling, and the evaluation of buckling strength is very important in structural design. In calculation of buckling strength, the Euler's method is famous and useful, so it is refered by some standard. For Standard for Structural Design in Japanese, we couldn't use that method directly, because timber material don't have the clear yield point. In our past study, we proposed a new method of evaluation method of buckling strengh, and evaluation method of yield strain from short-column compression tests. In this study, we would apply that method to LVL of Japanese Larch. For the material, the wood species is Japanese Larch, the strength grade is 100E in Japanese Agricultural Standard(hereinafter called "JAS"), and the cross-section is 45×90 mm. As a material tests, we conducted short-column compression tests and bending tests based on Japanese Agricultural Standard of plywood and LVL. We compared the yield strain from the both tests, and defined as a yield strain from short-column compression tests. The yield strain was almost 2400×10-6. Next we conducted compression tests with different length or different slenderness ratio with 50, 60, 79, 80, 100, 130, 150 and 190. From the compression tests we would get the some types of bucking strength, the one is the strength from southwell's method(σ1), the second is the maximum stress(σ2) and the last is yield buckling strength (σ3). As compared the σ1 and σ2, the both values would be almost the same. When we compared the σ1 and σ3 with large slenderness ratio, both values are almots the same. On the other side we could clear difference in both value in small range of slenderness ratio. The border would be called "limit slenderness ratio" theoretically. Then we focused on the ratio (σ2/σ3), between the 50 and 80 of slenderness ratio, we could find a difference between σ2 and σ3, and the ratio was bigger than 1.2. In the area from 80 to 190 of slenderss ratio, the ratio was almost 1.0. As a result, we could define the limit slenderss ratio was 80 in this study. In fact the elastic buckling occuered over 80 of slenderness ratio and the yield buckling occuered under 80 of slenderness ratio. Finally we would apply the Euluer's method for the evaluation of elastic buckling, Tetmjer's method and for the yield buckling. Then we could get the lower limit strength with combination of both method. In this method, we used 5% lower limit value in JAS for the Young's modulus in Euler's method, experimental 5% limit strength for the strength in Tetmjer's method.
The stiffness and shear capacity of nailed sheathed shear walls are calculated by summing up the resistance force of nails assuming that sheets don't buckle and are not damaged by shear. High strength shear walls are designed based on calculation without considering the limitation of the existing formulae. The limitation of this formulae is determined in this paper based on experimental and analytical studies.
Regardless of the material type and size of sheets, the followings are experimentally confirmed.
1) The critical shear buckling stress increases as the amount of nails onto sheets increases as shown in Fig. 3, because the boundary condition changes from simply-supported edges to clumped supported edges of sheets.
2) The shear strength of sheets decreases when sheets buckle in an early stage as shown in Fig. 4, because ununiformed shear stress in sheets distributes due to the deformation of shear buckling.
3) The maximum nailing pitch on a sheet to be attached to a stud for stiffening against shear buckling is N50-@300mm which is obtained by FEM eigenvalue analyses as shown in Fig. 8.
4) The critical shear buckling stress of sheathed shear walls stiffening with studs are estimated to be 2τcrp as shown in Table 4, where “τcrp” is the critical shear buckling stress of no stiffening sheathed shear walls with simply-supported edges.
5) The formulae to calculate the value of “τcrp” is presented by regression analysis from the calculation chart in Fig. 11.
6) The formulae to determine the limitation of the calculation method to design high strength shear walls are presented in Eqs.(3)-(5).
7) The quick reference table for plywood sheets are presented in Table 5, eliminating the need of examining the shear buckling.
In seismic evaluation methods based on limit strength calculation, a shear force with a one-to-one correspondence with a load-bearing element is defined, and the shear force of construction only adds the restoring forces of the element. However, the specifications of traditional joints and element position may vary, and the calculation method does not depend on these specifications. Some previous studies have considered the specifications of traditional joints such as column-to-beam (Sashigamoi) joints based on element experiments and simulation analysis. However, the influence of element position on the structural properties and the behavior of traditional wooden frames with large section beams (Sashigamoi) based on multi-span frame experiments has been addressed in few studies. Japan has experienced numerous earthquakes, and there are many reports of traditional wooden structures collapsing because of earthquakes. However, many traditional wooden structures remain sound and unaffected and are extremely interesting. Evaluation of the seismic performance of such traditional wooden buildings may be significant in preventing damage to buildings and ensuring safety. Against this background, this paper presents the results of static cyclic loading tests and simulation analysis for four traditional wooden frames in order to understand the seismic performance of frames with uneven large section beams (Sashigamoi) and to clarify the influence of the beams and shapes of fitting-type joints on the behavior of the whole frame. Major findings of the present work are as follows: (1) First, static cyclic loading tests were conducted on four traditional wooden frames; the number of frame spans, the presence or absence of large section beams (Sashigamoi), and the position of beams were considered as the parameters. Two-span frames underwent column splitting or column breaking more readily and with smaller deformation than in the case of one-span frames. In addition, the shear forces exhibited directional dependence, which is attributed to the asymmetry of the frames or the shapes of the column-beam joints. (2) Second, a method for modeling traditional fitting-type joints was developed. This method can be used to analyze traditional wooden frames with large section beams (Sashigamoi). Simulation analysis results were in good agreement with the test results. (3) Finally, a parameter study about the aspect ratio of the frame, large section beam position, and beam height distance was carried out, and the restoring force was verified. The smaller the beam height distance, the smaller was the difference in the restoring force with the loading direction.
Vertical wall reinforcing bars of a boxed wall precast concrete structure in Japan must be anchored straight in the foundation beam. Sometimes, the beam width may not be sufficient to develop anchorage strength in the concrete although the AIJ (Architectural Institute of Japan) Standard for Structural Calculation of Reinforced Concrete Structure requires minimum concrete volume for the development of deformed bars. A series of pull-out tests were carried out to investigate structural performance of anchored bars using various prototype specimens. The purpose of the test series was to study the effect of various parameters and to clarify the failure mechanism. A new series of tests were carried out using high strength deformed bars and varying the foundation beam widths. The anchored bars were pulled out from the base beam exhibiting the relationship between maximum bond stresses and flexural stresses with in the beam. It can be concluded as follows: (1) D19 (diameter 19 mm) deformed bars of Grade SD345 and SD685 (nominal yield stress of 345 and 685 MPa) can be anchored with a development length of 40d (d: bar diameter) for the precast reinforced concrete box-wall construction. When deformed bars are anchored using sheath pipes after construction of the beam, the sufficient development strength was achieved. (2) D19 deformed bars of Grade SD980 were pulled out of the beams of 180, 220, 330, and 440mm widths. (3) Bond failure of a deformed bar developed from the beam top and progresses to deeper region with load. (4) Flexural compressive stresses in the foundation beam increased bond resistance of the deformed bars. (5) Flexural tensile stress or strain of concrete in the foundation beam had less influence on the bond resistance along a deformed bar. (6) The beam width had not much effect on the development strength of a deformed bar within the foundation beam. (7) The development strength of deformed bars was proportional to the flexural compressive stresses in the foundation beam. (8) The development strength increased at a higher rate for beam width less than 180mm, but the increase rate became smaller for the beam width more for 220mm to 440mm.
In Japan, square steel tubular columns are widely used. When the building is subject to a seismic load, columns will subject axial force with antisymmetric bending moment simultaneously. Therefore, it is important to design the column under these combined loading in the ultimate limit state to guarantee the safety. Recommendation for Limit State Design of Steel Structure (LSD) specifies the requirements for columns to guarantee sufficient strength and ductility. The plastic deformation capacity of the columns that are subjected to compressive axial force with one end monotonic bending moment are ensured more than 3 by LSD. However, specific deformation capacity of the column that are subjected to compressive axial force with monotonic antisymmetric bending moment is not shown. Test results that can confirm the appropriateness of LSD requirements for square steel tubular column are limited. It is necessary to gather more data of maximum strength, deformation capacity, and elasto-plastic behavior of square steel tubular columns by testing. Moreover, column that is subjected to compressive axial force is important to take into account second-order effects. In this study, testing where axial force with monotonic antisymmetric bending moment are applied to the columns simultaneously are conducted. Maximum bending moment, deformation capacity, and second-order effect that will be caused by Pδ moment were evaluated from the test results. Comparison between LSD requirements and test results were also shown. From the test results, followings are found. 1) Three types of collapse mechanism are confirmed. i) Local buckling occurred at one end of the column determined the ultimate state and deformation capacity. ii) Pδ moment determined the moment capacity at the loading point. After the maximum bending moment, local buckling occured at the maximum deflection point and it determined the ultimate state and deformation capacity. iii) Pδ moment determined the moment capacity at the loading point; increment of the bending deflection determined the ultimate state. Local buckling was not observed during the testing. 2) When the value of ny·λc02 is larger than 0.25, second-order effects determined the plastic deformation capacity. Plastic deformation capacity R of the columns that were determined by Pδ moment had a linear relation between ny·λc02. When the value of ny·λc02 is smaller than 0.25, plastic hinge was formed at the end of the column and determined the collapse mechanism. Width-to-Thickness ratio equals to 21.7 that was used in the testing and collapsed by local buckling had a plastic deformation capacity around 3.5. 3) Plastic deformation capacity of the square steel tubular column will be determined by either local buckling or Pδ moment. It was found that deformation capacity of the columns that were determined by Pδ effects have a linear relationship between ny·λc02; therefore, it is also important to evaluate quantitatively the plastic deformation capacity which is determined by local buckling. 4) Plastic deformation capacity greater than 3 were observed even if the current LSD limitation was not satisfied. However, from the point of view of collapse mechanism, LSD limitation can form a plastic hinge at the end of the column which is expected in design.
When designing important structures such as industrial plants and public facilities, it is necessary to ensure their safety against accidental or intentional explosions, which happen rarely but can cause severe damage. In particular, the fracture modes of reinforced concrete (RC) slabs subjected to blast loadings are characterized by spalling, which is caused by a combination of reflected tensile stress waves and diagonal cracks created along the maximum shear stress surface, as shown in Photo. 1. To protect the lives of humans inside a structure under such conditions, it is necessary to prevent the launch of concrete fragments that accompanies spalling. Therefore, reducing spalling damage is the most important problem faced by the designers of blast-resistant RC structures. In a previous study, we clarified that slurry infiltrated fiber concrete (SIFCON) exhibits better spall-reducing performance than normal concrete and other fiber-reinforced cementitious composites (FRCCs). However, it was also confirmed that the SIFCON, as well as the other FRCCs, had no effect on reducing crater damage during a detonation. Therefore, for more efficient blast-resistant strengthening of RC slabs using SIFCON, it may be necessary to adapt the SIFCON to a region in which the occurrence of the spalling damage inside the RC slab is expected. The objective of this study was to develop an efficient blast-resistant strengthening method of RC slabs using SIFCON; to this end, experimental investigations were conducted to evaluate the blast resistance of RC slabs in which the concrete near the rear was replaced with SIFCON. The total thickness of the RC slabs was fixed at 100 mm, and the behaviors at different thicknesses of 0 (un-reinforcement), 25, 50, 75, and 100 (overall-reinforcement) mm of the SIFCON layer near the rear side was studied, as shown in Fig. 1. Contact detonation tests were carried out using two different amounts of explosives (SEP) 100 and 200 g. After the tests, the fracture behaviors of each specimen were observed in detail, and then the sizes of the local failures in all specimens were measured and compared. Further, the spall-reducing mechanism of the RC slabs with SIFCON cladding was qualitatively discussed, based on the propagation behavior of the stress wave in a one-dimensional wave model and the punching-shear strength of the SIFCON layer. The main results obtained are as follows: (1) The SIFCON cladding effectively reduced spall damage of the RC slabs under conditions in which the failure modes of un-reinforced RC slabs with the same thickness were “spalling” and “perforation”. (2) Both, the damage inside the SIFCON layer and the spall damage created in the rear side, decreased upon reducing the thickness of the SIFCON layer. However, even if the SIFCON layer was not perforated, the scale of the spalling damage in the normal concrete layer became almost as large as that in un-reinforced RC slabs. (3) When the thickness of the SIFCON layer was sufficiently smaller than the wavelength of the stress wave, spalling damage in the rear side of the RC slabs with SIFCON cladding was reduced by a combination of the following three mechanisms: (a) Since the tensile stress attributed to the reflected tensile stress wave became small inside the SIFCON layer, serious spalling damage did not occur in the rear side of the slab. (b) Diagonal cracks, which formed in the normal concrete layer, did not penetrate the SIFCON layer and propagate along the interface between the normal concrete layer and SIFCON layer because the punching-shear strength of the SIFCON layer was considerably higher than that of the normal concrete layer. (c) The launching of the spall fragments formed inside the normal concrete layer was prevented by the SIFCON layer of high punching-shear strength.
Verification on load-bearing performance for a steel welded joint, which is usually used for a beam-column joint in a steel rigid frame, is of importance to secure structural safety of steel building structures. Many researches using experimental, numerical and theoretical approaches on that have been conducted since the Kobe Earthquake (1995) in Japan, when many welded joints were brittlely fractured. The verification methods used at actual structural design have been established, because the seismic performance was clarified by their valuable research results. On the other hand, there are few past researches on the fire resistant performance, hence that cannot be verified at fire resistant design for the steel structures. Main purpose of this study is to clarify the load-bearing capacity of the welded joints at high temperature and accumulate the experimental date using for the fire resistant verification. The tensile tests under a condition on constant temperature and monotonic loading were conducted. After heating specimens by an electric furnace, tensile force was gradually applied for them. The specimens including a full penetration (FW specimen) or partial penetration (PW specimen) welded joint were fabricated. The base metal and weld material are JIS SN490B and JIS YGW11, respectively. For comparison of the experimental data of the welded specimens, the specimen without the welded joint (P specimen) was used for the experiments. All specimens were fabricated into a tapered shape. The welded joint was arranged at the minimum sectional area of the tapered shape specimen. The test temperatures from ambient temperature to 800 °C were used. For the FW specimen, the tensile tests were additionally conducted up to 900 °C. From a series of the tensile tests at the high temperature, the following experimental results were obtained. The maximum load of the specimen gradually decreased with the test temperature increase. At the ambient temperature, the specimens ductility fractured after the peak of tensile load. On the other hand, they did not fracture after the peak at the high temperature and exhibited residual strength. In this region, the tensile load gradually decreased with the deformation increase. The PW specimens fractured at the weld metal in the partial penetrate welded joints. The FW specimens over 800 °C fractured along fusion lines between the weld metal and the heat affected zone, otherwise they fractured at the base metal. However, the specimens fractured at the welded joints possessed the sufficient load bearing and deformation capacity at the high temperature. From specimen observations after the tests, large residual plastic deformations in the tapered shape specimen and necking at the fractured section were observed for all specimens. The reduction factor on the tensile strength of the specimen including the welded joint, which is fundamental information to verify the fire resistant performance of welded joint, was estimated by the obtained experimental results. From the reduction factor curves at the elevated temperature, it was confirmed that both welded joint and base metal possessed the similar reduction factors over 600 °C.
Public buildings in Japan are being increasingly constructed from wood. Timber-based buildings have been considered from various perspectives, including management of forest resources and environment concern. Large-scale buildings in Japan are needed to be fire－resistive or quasi-fire-proof constructions to withstand fire damage. If a fire breaks out a large-scale timber building, the residual strength of structural members exposed to fire must be known for the fire safety. For this purpose, study on physical properties of wooden structural members are important and influence of charring, temperature shift under heating and water content at normal temperature of wooden structural members have been studied. However influence of water content on the structural properties of wooden members under high temperature is not clearly. In this paper, Cryptomeria Japonica, a softwood commonly used in timber engineering, and Zelkova serrata, a hardwood normally used in traditional large buildings, were heated up to 95°C. The Young's modulus and bending strength of two species were measured at the elevated water content and temperatures. The results provide an engineering basis for the structural fire safety design of large-scale timber buildings. The following properties of the woods were analyzed and determined. 1. The effect of water content on Young's modulus and bending strength at elevated and normal temperatures. 2. The effect of heating on Young's modulus and bending strength at elevated water content. 3. Relationship between Young's modulus and bending strength in heated moisture state wood. In the bending experiment, the mechanical properties of heated Cryptomeria Japonica and Zelkova serrate on a scale of 1 to 4 below water evaporation temperature (room temperature, 50°C, 80°C and 95°C). The specimens were hewed from the two logs without knot and sized 20mm square and 320mm span (Fig. 1). The water content of specimens was from 1 to 150% and divide into four groups. Group1 is low water content, under 5%, Group2 is medium water content, between 5% and 15%, Group3 is other medium water content, between 15% and 30%, Group4 is high water content, over 30%. We used, as needed, a small dry kiln heated to 60°C to drying. The bending test conformed to “The examination method for the bending strength” stipulated by JIS Z 2101 and was conducted in a compression testing machine with a heat-controlled chamber (Picture1). A flowchart of the experimental procedure is presented in Fig. 2. The Young's modulus of two species at elevated water content and temperatures, was largely affected by water content over 5% and heating temperatures 80°C or higher. The bending strength at normal temperature or higher was highly dependent on water content, however two species show different declining trends with the rise of water content and temperatures. The correlation between Young's modulus and bending strength of Cryptomeria Japonica and Zelkova serrate keep to the same with the rise of water content and temperatures. This study reports an experimental assessment of structural fire safety on large-scale timber building.
Several questions are submitted here in this discussion. The questions are concerned with the following items. The items are (1)details of the test setup, (2)rotational displacement of the loading jig, (3)equilibrium of forces, (4)accuracy of drawings and (5)mechanical logic of the formulation. The discusser asks the authors to answer the questions.
The authors thank Prof. Katsuki Takiguchi for his discussion, and the answers are as follows: (1) The details of test setup agrees with the practical conditions. (2) The rotational displacement is not negligible because small horizontal displacement about from one to two millimeter is evaluated. (3) The equilibrium of the loading jig is archived with couple of forces from the nut and concrete. (4) The drawings is correcting in this answer. (5) Previous experiment is indicated the effect under tri-axial compression on the concrete compressive softening characteristics.