Nonlinear Dynamic Response Analysis Of Frames Reinforced With Steel Bars In Different Strength Grades Under Bi-directional Earthquake Waves’s Input

The new edition Code for Design of Concrete Structure has treated HRB400steelbar as the leading reinforcement and recommended it to the engineering fields. TheHRB335steel bar will be eliminated in a few years. As China’s steel consumption ishuge and it is lack of natural resources,the new code introduced a higher strength graderebar, that is HRB500, for the consideration of sustainable development andenvironmental protection. Although a certain mount of reinforced concrete componentswith HRB500bars have been tested,yet seismic analyses to the whole structures withhigh strength bars are not enough. This academic team has done some seismicresearches to2-D frames reinforced with HRB335,HRB400,HRB500separately,and hasalso input several earthquake waves to a certain single degree of freedom system toverify that the stiffness and seismic force also declined rapidly in multi degree offreedom system which were reinforced with higher strength grade rebars.However in areal,complicated3-D structure, how the stiffness and seismic force will change alongthe height is to be studied.What’ more,China has developed a new kind of high strengthsteel bar,namely HRB600, but seismic research to frames reinforced with HRB600isstill at a blank stage.Considering all the reasons mentioned above,this paper has donesome nonlinear dynamic response analyses to two batches of frames(total fiveframes)located in intensity region8(0.3g).The first batch of frames were designed basedon the principle "Substitution of the Same Design Strength".That means the author got aframe reinforced with HRB335firstly and then got another two frames reinforced withHRB500,HRB600separately according to this principle to investigate the seismicresponses not considering the requirements of minimum reinforcement ratio andserviceability limit.The second batch of frames reinforced with HRB500and HRB600steel bars separately were strictly designed according to the codes.Then the author usedthe software "Nonlinear Analysis and Performance Assessment for3DStructure"(PERFOM-3D for short)to investigate the seismic response of these twobatches of frames,and got main conclusions as following:①Although to take high strength steel bars could reduce the consumption ofsteels,the requirements of minimum reinforcement ratio and serviceability limit wouldcounterweigh the advantage of high strength steels to some extend. ②In terms of the overall responses like the most unfavorable story drift angle andthe maximum top displacement,the two batches of frames are nearly the same,that is theresponse of frames reinforced with high strength steel bars is larger, because thestiffness of frames reinforced with high strength steel bars decline rapidly;most of theends of beams are yielded under the bidirectional rare earthquakes’input in both of thetwo batches of frames;the two batches of frames have the same trend in rotationaldeformation factors of beams and rotation angles of columns which means the rotationaldeformation factors of frames reinforced with higher strength steel bars are smaller androtation angles are larger.③From the perspective of the material property,the high strength steel bar has aside effect on the seismic performance of the whole structure,but if designed andconstructed in strict accordance with the code,the seismic response of structures wouldnot be too large and could meet the expected goals.