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Seismic performance of steel building structure is closely related to selection of the design performance level, as well as quality of fabrication, in the case of welded moment resisting frame. The current institution system to certify the quality assurance at shop welding stage is reviewed and discussed. Future subject on the steel fabrication, necessary to grasp more accurately the seismic performance, is proposed.

This paper deals with the effects of strain rate on the mechanical properties of base metals, buttwelded joints, high-strength bolted joints and regular bolted joints due to cyclic reversed loadings. The increase of the yield strength and the ultimate strength of the base metals was significantly observed under the monotonic loading conditions. However, under cyclic loading conditions, the effect of strain rate on the mechanical properties were various in different joint types. From the results, it can be seen that the particular attention should be paid on the design of bolted joints, especially, in stell structures with short natural periods.

This paper refers to deforambility of double-Warren truss tower structures composed ofcircular hollow sections, which are widely used in constructing steel towre structures. In currentdesign practice, the structures are regarded as being collapsed as a whole, when buckling in aprimary compressed member occurrs, strength and deformability of the structures are not takeninto account in the post buckling range. In order to improve the durability of the structure, itis desired to design so that buckling of the primary member does not lead to the collapse of thestructure.A method to improve deformability of the structure by adding bending resistant members isproposed. In order tomake clear stability and deformabilkity of the proposed structures in com-parison with those of ordinary truss structures, an experimental investigation was carried outusing subasseinblages of truss structure.

This paper presents the distribution properties of the shear forces of steel tower structuressubjected to earthquakes from the results of shaking table experiments.Dynamic properties of the steel tower itself were initially examined by using a rod model, alatticed tower model and the models with additional lead weights which were installed at differentlocations of the original models, so as to generate various shear force distributions. From the re-sults, the shear forces of models predominantly viblating in the fundamentary mode were greaterthan which specified by the latest Japanese building code, at the middle height part of the mode.Whereas, model predominantly viblating in the secondary mode showed similar shear force distri-butiona as the building code, but the relative response of the top of the model was greater, whenthe mass of the top was smaller.Secondary, a coupled model consisted of the towers and cables simulated actual power trans-mission tower lines was tested in order to assess the effect on dynamic response of biaxial excita-tions. From the results, it has been shown that dynamic response of individual towers are re-markably influenced by the stiffness of the cables at the longitudinal excitation, whereas the re-sponse at the transverse direction was smaller caused by damping effect of cables. And thus, aseismic safety of actural power transmission towers subjected to the longitudinal excitationsassessed by taking account of the existence of electric lines.

Stress (or strain) rate effect in several steel structural joints is examined to assess thestructural safety of the joints against earthquakes or gusts. High speed tensile loading testwas carried out with several range of loading speed, by using high tension bolted joints ofequal leg angles and split tee joints as well as galvanized normal steel bolted joints.From the experiment, mechanical properties of the joints under high speed loadings wascalculated and was compared with the properties of the base metals under statically loadingcondition. From the comparison, it has been observed that the high tension bolted jointsdesigned by applying with friction mechanism are inferior in strength ratio to the angleswhich are applied to the structural members under high speed loading conditions, and itcan be followed that careful attention should be paid to safety of the structure, composed ofthe joints against excitations with comparatively large velocities.

Inelastic behavior of welded steel beam-to-column connections with different details havebeen investigated experimentally, under cyclic reversed loading conditions. The attentionwas focussed to clarify how to improve the deformability of the connections without distinctdeterioration of load carrying capacity, from the view point of the durability of the momentresisting frames in the event of earthquakes. From the results, panel zones can be effectivelystrengthened by applying the stiffener plates of adequate thickness, such as diaphragms, vertical stiffners and/or the panel flanges. And the particular attention should be paid to lowcycle fatigue phenomenon at the critical section of the connections under cyclic loadings.

Load carrying capacity of ordinary double-Warren truss structures under horizontal andvertical loads were examined by experimental investigations. The experimental results arecompared with the results obtained from the past experiment by using identical specimenssubjected to the horizontal loading. Also, the stiffness of frames is analytically evaluatedregarding slippage of bolt connections.

This paper deals with an experimental investigation with respect to buckling behaviorand hysteresis characteristic of the subassembkages of typical double-warren truss towerscomposed of cylindrical hollow sections, subjected to monotonic and cyclic horizontal forces.Four types of subassemblages of the typical tower structures, which were designed andfabricated with and without slant and horizontal struts, were prepared for the experiment.Effect of the connecting method of the elements on buckling strength and restoring forcecharacteristic of the structure has also been examined.Slippage of the bolted connection causes reduction of shear stiffness of the structureand buckling strength of the compressive members, although the structure possesses fairlywell energy absorbing capacity.

This paper deals with an experimental investigation to estimate the influence of strain rateon the strength and ductility of several steel structural joints due to high speed monotonic tensileloadings.The galvanized bolted joints used for towers as well as the ordinary joints in buildings, thatis, the butt welded joints and the high strength bolted joints, have been tested and the resultswere compared with those of the base metal of mild steel.From the test results, it has been concluded that, since the mode of joint resistance and thegeometry of the bolted joints can affect remarkably the yield and the ultimate strength underhigh speed monotonic loadings, the strengths of the joints may not be directly estimated fromthe result of the base metal.

In this paper, a newly developed forged diaphragm is proposed to improve the fabricatingprocedure in the steel panel zone such as grooving and scalloping when the column ofrectangular hollow section are connected to the beam of wide flange section in the momentregisting steel frame.Initially, mechanical property of the diaphragm was decided to develop the sufficientductility performance by suitable heat treatment after forging and the specific groove shapewas also decided to insure the good weldability in the connection, through the experimentalinvestigation.Secondary, the subassemblage test using the forged diaphragm was performed to assessthe load carrying and the energy dissipating capacities of the connection in the weak beam-strong column type structure in the event of earthquake.This research shows that sufficient strength, ductility and stiffness of the connection canbe exhibited in the proposed beam to column connecting method, even in the highly seismicregions.

Strength and ductility of latticed steel towers can be considerably affected by the magnitudesas well as the directions of external forces caused by earthquakes and wind.An experimental investigation was carried out in order to examine the properties of overallload-deflection relationship and instability of typical space tubular towers subjected to monotonicor cyclic horizontal loads which act on the tops of the towers in the diagonal directions.The experimental results are compared with the results obtained from the past experiment byusing identical specimens subjected to the horizontal loading along the principal axes of the towersections, and the characteristics of the stress distributions of the towers are discussed. Also, buckling strength of the components are estimated by taking into consideration the actual bound-ary conditions, under combined bending and axial forces.

This paper deals with the strength and ductility of very shallow embedded type steelcolumn-to-footing connection subjected to cyclic reversed bending moments as well as columnand vertical-brace axial forces.Experimental investigation was focussed to inspect the effect on the reinforcement of theadditional concrete cover upon the base plate to improve seismic resistant capability of the con-nection. The result showed that the connection embedded to about 0.6 times of the steel columndepth exhibits the fairly well ductility and possesses the higher ultimate strength than that of thesteel column, and thus the additional concrete cover contributes to stiffen the exposed column-to-footing connection, together with the longitudinal reinforcement of the concrete column stubarranged with proper separations around the base plate.An analytical model has been proposed to estimate the ultimate strength and rigidity of theconnection under the complex loading conditions which simulate seismic behavior of such connec-tion in the large scale industrial steel structure.