Most cracks in concrete structures are initiated first by the largest principle stress, and propagate under subsequent shear and transverse compression or tension. A biaxial testing device, with which the vertical and horizontal load as well as displacement can be independently controlled by closed-loop servo systems, has been developed in order to establish the shear behavior in cracked concrete. The shear tests on specimens containing narrow cracks (fracture process zone introduced by the tensile test in displacement control) have been carried out maintaining either normal displacement or load across the crack surface constant. The relation of normal and shear stresses to crack opening and sliding displacements was discussed and distinguished by the boundary conditions of the normal direction across the crack surface. Several expressions which give shear retention factor, β, have been derived based on biaxial test results.

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The effect of high-temperature curing at an early age on the strength development of concrete using moderate-heat portland cement was quantitatively studied. High-temperature curing conditions were set so as to give systematic variations in the temperature-time factors. As a result, the integrated value of curing temperature during the period having a significant effect on the strength development was proposed as a parameter that expressed the degree of high-temperature curing. The effect of high-temperature curing on the strength development of concrete using moderate-heat portland cement could be exactly predicted with the integrated value of curing temperature during the period from 0 to 3 days.

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Tensile and compressive creep of epoxy resin floor coatings was first measured at four levels of stress at 5,20 and 35℃ for making clear the mechanism of blistering of epoxy resin coated floors, and the empirical equation of expressing creep behavior was obtained from the observed creep data. Then, the development of blisters of epoxy resin coatings applied on concrete substrate was experimentally measured at the same three temperatures. The height of the blisters was estimated by FEM calculation considering the creep behavior of the epoxy resin floor coatings. The calculated values are approximately accordance with the observed ones, and it is concluded that growth of the blisters is closely related to the creep of the epoxy resin coatings.

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Relationships between measurements of nondestructive testing and quality characteristics of concrete relative to durability were investigated in order to establish direct quality inspection methods of concrete in structures. The ultrasonic, rebound and combined methods were used for the nondestructive testing. Correlation between the pulse velocity and the tensile strength, dynamic modulus of elasticity, bulk density and water absorptivity were stronger than the one with compressive strength. The combined method was effective to increase the reliability of testing to predict quality of concrete in structures.

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A stochastic model for predicting the typhoon wind damage to cladding of residential houses in the Tohoku District has been developed. The model consists of 'typhoon model', 'surface wind model', 'local pressure model', and 'wind resistance model'. In the 'surface wind model', the effect of local topography on wind speeds is considered. In the 'local pressure model', the roof geometry is classified into two groups, I.e. gable and hip roofs, and the local pressure coefficient is specified for each group. In the 'wind resistance model', the probability density function of cladding strength is represented by the lob normal distribution, which is predicted from the damage rate of cladding due to Typhoon 9119.

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A structural load varies in space and in time. When more than one load act on a structure, the maximum intensity of the combined load effect needs to be evaluated. Turkstra's rule is often used because of its simplicity. However, its theoretical reasoning and applicability are still in question. This paper presents the theoretical expressions of the cumulative distribution function of the maximum intensity during a reference period taking the temporal variation of load intensity into account. Numerical examples show that, while Turkstra's rule provides an unconservative estimate, the theoretical expression provides a fairly good estimate regardless of the statistical characteristics of the load processes.

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It is necessary to consider the frequency dependent behavior of viscoelastic material in order to simulate seismic behavior of structures with viscoelastic dampers. Three dynamic mechanical models for viscoelastic material, the spring-dashpot model, the fractional derivative model and the fading memory model are examined in frequency and time domains. A generalized fractional derivative model is proposed to consider frequency dependent for wide frequency region. The spring-dashpot model and the fractional derivative model are expressed by the fading memory model with an adequate memory function. Load-deformation relations of calculated results using three models were in agreement with experimental value respectively. Three models explain well frequency dependent characteristic of viscoelastic material.

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A simple quasi-dynamic method is presented for computing the impedances of pile groups installed in a homogeneous surface stratum lying on rigid bedrock. This method for not only axial and lateral but also rotational and coupling impedances of pile groups is considered in the simple expression with exponents from stiff and short piles to flexible and long piles. This method is easily executed without much computaional effort by the simple expression. The verification of this method is performed from comparison with the results of the rigorous solution. This method is sufficiently accurate and readily useful in practical application.

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Optimum designs are found for elastoplastic trusses subjected to multiple loading conditions including cyclic loads. A new formulation is presented for the optimization problem under stress and strain constraints, and the optimal solutions are found by using a gradient-based optimization algorithm. The sensitivity coefficients of the responses with respect to the design varibles are found by using the author's incremental method of design sensitivity analysis. It is shown for the case of simultaneous yielding that the yield condition of only one yielded member may be used for updating the sensitivity coefficients. Optimum designs are found for symmetric trusses under constraints on strains and stresses, and the effects of loading conditions and the admissible strain levels on the optimum design are discussed.

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An earthquake-proof pile composed with a main pile and a short outer sheath pile is proposed in this study. It is expected that the outer sheath pile shears the most part of the horizontal load in an earthquake whereas the main pile is against the vertical load mainly. This paper presents the experimental result of model earthquake-proof piles done by changing the outer sheath pile length, and also a calculation method for the pile system of this type. These results suggest that the horizontal deformation of the pile and the bending moment in the main pile could decrease remarkably, even if the outer sheath pile length is set up comparatively short.

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The purpose of this paper is to study how the stiffness and weights of the support structure influence the response of the large span dome with seismic isolation system, when it's subjected to horizontal earthquakes. This system is applied to a latticed dome with about 300m span, and dynamic response analyses with various conditions are carried out to make it clear. From the results of the numerical studies, it is confirmed that the seismic isolation system with hysteresis dampers can almost reduce the vertical and horizontal acceleration responses of the dome, independent of the stiffness and weights of the support structure.

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The evaluation of earthquake resistant capacity of traditional timber houses in consideration of the floor stiffness and grid lines of bearing walls is discussed. The result may be summarized as follows: The ultimate horizontal resistant force with hard stiffness floor is estimated from the one with soft stiffness floor. The minimum value of partial wall-length ratios of the resisting wall is independent of the wall-length ratio of the resisting wall. The resistant force calculated with the minimum value of partial wall-length ratios of the resisting wall has less error than the one calculated with the wall-length ratio of the resisting wall in comparison with the ultimate horizontal resistant force.

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Two model structures are presented. One model structure consists of a rigid plate and two springs. Each spring has the same tri-linear P-δ relation. Relation between two dimensional forces M_x, N_z and two dimensional deformations Φ_x, δ_z is examined. To formulate the restoring force-deformation relation, the concept of plastic potential and Prager's kinematic hardening rule are used. Using the theory of plasticity, two-dimensional non-linear behavior of the model structure can be perfectly described. The other model is a square section. The meterial of the section doesn't transfer tensile stress, and is rigid-perfectly plastic in the compressive strain region. Relation between forces M_x, N_o and deformation φ_x, ε_o is examined. Some part of restoring force-deformation relation of the model structure is far different from the rigid-perfectly plastic theory. Possibilities and difficulties to describe the multi-dimensional non-linear restoring force characteristic of structures by using the theory of plasticity are shown.

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The authors proposed a new calculation method of long-term deflection of floor slabs. By this method, long-term deflections can be calculated under a unified conception and method between prestressed(PC), partially prestressed(PPC), and reinforced concrete floor slabs. It is an application of the "Load Balanced" design method. In the method, for the "residual load" which is the difference of total design load and the balanced load, the long-term deflections are calculated as a reinforced slab. In the study a long-term deflection experiment was conducted using two PPC concrete slabs and one reinforced concrete slab having 13 meter effective span. Using the proposed model, the calculated deflections were compared with experimental ones. As a result, the proposed method can calculate long-term deflections of PC and PPC floor slabs in good accuracy.

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The estimation of crack width is one of the most important tasks in designing partially prestressed concrete (PPC) members. However, this task, which includes calculation of crack spacing, average steel stress etc., is very tedious using current existing procedures. In this paper, relationship between crack width and hypothetical tensile stress was derived in order to simplify control of crack width in reinforced conctrete and PPC members. The hypothetical tensile stress is calculated on the assumption that the entire section is still effective even after cracking has occurred. The instantaneous and long-term crack widths are calculated by using the PPC Recommendation of Architectural Institute of Japan. Factors which had been taken into account in developing procedure of this method are: concrete strength, ratio of reinforcement, depth of beam, concrete cover depth, prestress, shrinkage and creep.

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An extensive research project has been devoted to finding out the causes and their physical relationships on brittle fracture of steel structures which were observed in the disaster of the 1995 Hyogoken-Nanbu Earthquake. This paper shows the results of one of the research subjects, in which full-scale fracture test was carried out to clarify the effects of material toughness and plate thickness on the plastic deformation capacity prior to brittle fracture. Major findings are as follows : material toughness in terms of Charpy impact energy gives a substantial effect on the plastic deformability, while plate thickness is of less importance ; statistical estimation shows the deformability of 95%-confidence level is scarcely dependent on assumed probability functions ; and numerical simulation for load-deformation curves of steel members indicates strain concentration and axial force in tension are significant for the deformability governed by brittle fracture.

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The authors have been studying the column-through type RCS (reinforced concrete plus steel) joints composed of web panel with opening, cover plate and triangle stiffener. The previous paper reported the relationship between shear strength and deformation capability of the RCS joint. The present paper addresses the investigation on the influence of stresses from the steel braces upon the joints, through loading tests conducted on a two-story, two-span RCS structure with steel braces. In addition to these tests, static elasto-plastic analysis was implemented, using the shear strength and shear deformation model proposed by the authors. The study results demonstrated that the stresses from the braces do not exert significant influence on the joint behavior and the analytical results agreed very well with the experimental results.

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The experiment of the column where steel existed on the way of height of the column was carried out under the condition that the structural form changed from steel reinforced concrete (SRC) to reinforced concrete (RC) in the column. The principal parameter was length of the steel which extended from the column base. The shear strength of the column with steel which existed below the half of height of the column was lower than that of the column without steel. The evaluation method of shear strength of the column where the structural form changed from SRC to RC was proposed.

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In order to propose the new design method for concrete masonry garden walls and strengthening methods for existing walls with poor seismic resistance, the field investigations of damaged and/or survived masonry walls during the 1995 Hyogoken-nanbu earthquake, damaged masonry walls during the 1997 Kagoshimaken-hokuseibu earthquake and existing garden walls in Oita City were conducted. As the results, the intersecting walls seems to play an important role for preventing significant earthquake damage. Based on the results of field investigation for the existing walls in Oita City, strengthening methods for masonry garden walls with poor seismic resistance are discussed in this paper.

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In order to aid design for environmental vibration, a simplified analysis for a floor slab is presented. The floor slab is supposed to be rectangular orthotropic Mindlin plates with Timoshenko beams. Then, the Rayleigh-Ritz method is adopted using Timoshenko beam functions with elastic restraint against translation and rotation as admissible functions. Since point supports are also considered, it is possible to create appropriate boundary conditions. Furthermore, a moving load and SMD (Spring-Mass-Dashpot) system are taken into account to stand for a moving body on the floor slab such as a forklift. Through a few numerical examples, some characteristics of the effective mass of Mindlin plate were examined to aid design for a TMD (Tuned Mass Damper). And dynamic effects caused by a moving load were found to be comparatively large when the plate was supported at only four corner points.

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