Caused by many reports on deterioration of reinforced concrete slabs on steel bridges, construction of composite girder bridges has decreased remarkably in the re cent two decades. But, the composite girder bridge seems to be supeior system even though it has RC slabs on it. The author is strongly expecting revival of the construction of composite girder bridges because an improvement of durability of RC slab is possible. In the development works of composite structures, experimental studies are carried out to verify the structural behaviors and strength. Some experiments in the works, however, seem to be unappropriate to discuss the actual behavior due to unreasonable selection of test specimens. Systematic plan of experimental tests should be built. when durability of a slab structures is investigated by fatigue testing, genaraly a pul sating load is applied. But, the author uses a wheel running machine because the actual slab is subjected to running wheels. By the two methods, the fatigue failure modes are quite different mutually even for the same specimens. Therefore, it should be recommended that an adequate testing machine has to be selected corresponding to the actual loading pattern on the structures.

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The present situations of design and construction on concrete filled steel tubular structures in Japan are described. The outlines of research works conducted in Kyushu University, such as the elasto-plastic behaviors of frames, the ultimate strength and deformation capacity of members, the limiting values of width(diameter)-tothickness ratio of cross sections, the stability and strength of slender columns, and the behaviors of truss frames are discussed. The design strengths of columns based on several foreign design standards are compared with Japanese design strength.

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This paper presents the results of an experimental work carried out to study the strength and behavior of concrete filled steel square tubular beam-columns under constant vertical and varying horizontal loads. The effect of filled concrete on the strength and behavior of the beam-columns is discussed. It is shown that the concrete filled steel tubular columns even whose width-thickness ratios are above a limiting value possess the good earthquake resistant properties, and the new limiting width-thickness ratio of a concrete filled steel tube can be relieved to 2 times that for a hollow tube.

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This paper presents the results of an experimental work carried out to study the elasto-plastic behavior of mixed frames composed of different classification of structural types of members, under earthquake loading. From the test results, it has become clear that the frame composed of SRC column and wide flange beam showed stable hysteresis loops, on the other hand the frame composed of RC column and wide flange beam showed much smaller deformation capacity than one of SRC column and wide flange beam, because these frames were not able to hold axial load and collapsed brittly.

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Buckling strength was experimentally investigated for the two types of mortar filled steel tubular columns, called bonded type and unbonded type. The difference between both types is in the loading manner and in the bond condition between the steel tube and the encased concrete. The tests were done on short and long composite columns with various slenderness ratio to find out the relationship between compressive strength and confinement effect for both types of long composite columns. Moreover a proposal for the prediction of ultimate strength were tried on the both-type mortar filled steel tubular long columns under axial compression. The results shows that there exists a significant difference in the stresses in steel tube depending on the bond condition, though the strength of the unbonded type is slightly larger than that of the bonded type.

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The objective of the present paper i s to investigate the mechanical behavior of composite girders with corrugated steel webs, where the effects of shear connectors are included. The shear connector types used here are studs, steel bars, and only holes without shear connectors. The 2-point bending tests i n which composite girders are placed in a simply supported condition and loaded in a static manner were conducted using the three types of shear connectors. Experimental results reveal that Bernoull i-Euler's assumption does not hold from the beginning of loading, and the studs and steel bars as shear connectors are effective in comparison with holes.

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This paper reports the deformation capacity of concrete filled steel columns on researching papers and the results of the bending shear tests of concrete filled steel columns. Then we derive a formula for limit rotation angle, axial force ratio and the diameter-to-thickness ratio. From the test results, we confirm the efficiency of the proposed formula in the estimation of the limit rotation angle, and we extend that formula to be applicable to high-strength materials, for concrete and steel.

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The hollow composite slab bridges are investigated to confirm the struc tural characteristics, especially in applying to the skew bridge with the skew angle of 30 degree. As the results of static rupture bending tests and finite element analysis, it is clarified that (1)this skew bridge has enough ultimate strength in comparison with the estimation of AASHTO, (2)the rubber bearing contributes to average the distribution of the reactive force and the deflection on the support line. Moreover, this paper proposes the rational skew span on basis of the investigation and introduces the examples of application to real bridges.

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The authors have investigated a mixed structure composed of reinforced concrete columns and steel beams. In this paper, two types of beam-column joints, through beam type and through column type, are proposed. In order to clarify the behavior of these joints under the earthquake loading, experimental tests were carried out by using eighteen specimens of beam-column model assemblages. The design procedures are proposed through the study on the shear strength, deformation and bar bond strength in the joint based on the test results.

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Uncertainties of the duration of strong winds and equations expressing fatigue damage induced by randam vibration make it difficult to evaluate windinduced fatigue damage. And the change of the load-deflection characteristics crossing the yield stress interferes with the brief estimation of elasto-plastic response . This paper concerns an expanded Typhoon Model, a brief calculation method of elasto-plastic response and the extrapolating fatigue equation for all stress levels including high stresses beyond yield point. As an example, the wind load, deflectiond and fatigue damage are calculated for the steel plate dampers to prevent the exceeding stress .

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The Authers have developed a deformed bar stud welding method (NS Stud welding) in which long deformed bar studs of 19 mm and 22mm diameters. This method can considerably reduce construction time and costs. Actual structures are used as example applications. One is the connecting struture of a concrete footing to a steel pipe pile foundation. Another i s an immersed tunnel element of a steel-concrete composite structure.

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A new type of a breakwater caisson made of composite members and reinforced concrete members is now under construction. This caisson called double cells is equipped by wave dissipation blocks. Several kinds of joints exist in the caisson where tensile force due to waves is dominant. To confirm mechanical properties of these joints, static pure-tensile loading tests are carried out. Through the loading tests, the joints have enough strength capacity for design load. However dislocation between steel plate and concrete is large when reinforcement for joints is not arranged.

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Effect of yield ratio on Box Section Members' Ductility were investigated by numerical analysis. To consider the effect of local buckling and to get the accuracy of this simulation, stress-strain relations getting from stab-column tests were used, and also the conversion theory were made to get equivalent width-thickness ratio from real width-thickness ratio using bleich's local buckling theory. From this simulation, low yield ratio improve the members' ductility in case of small width-thickness ratio, but in case of large width-thickness ratio yield ratio is not effective on the members' ductility.

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