Study On Performance Of The New-type Steel-concrete Composite Joint And The Composed Frame Structure

The survey on Wenchuan Earthquake showed that the damages of frame structure weremainly be included with column end damage and joint damage. The damage of beam endswas rarely seen. Due to the failure of implementing specified “strong column-weak beam”yielding mechanism, many buildings in Wenchuan collapsed. In addition, after the damage ofregular reinforced concrete frame structures, even if the reinforcement and reutilization wasapplied, the residual deformation of the original structure was often too hard to repair.Besides, the reinforced steel bars and newly placed concrete showed stress lagging, difficultreinforcement and great costs. The seismic capacity of conventional reinforced concreteframe structure in China should be improved.This research invented a “steel-concrete composite joint”, which is constituted by steelplate, concrete-filled steel tubes and longitudinal reinforcement of column. Friction slidingwill be generated between concrete-filled steel tubes and steel plate, which will produceenergy dissipation. The new-type frame structure designed in this research has steel-concretecomposite joints at both ends. Prestressed tie rods were installed in the frame at oppositeangles in two-ways. This research adopted experiments as the main approach, supplementedby theoretical analysis and numerical calculation. The long column, short column and framestructure of column ends with steel-concrete composite joints were analyzed. Moreover, therepairing experiment of damaged new-type column and new-type frame was implemented.The result presented that the new-type column and new-type frame presented significantdeformation capacity and seismic performance, as well as efficient repairability.To detect the performance of steel-concrete composite joints, the research conductedexperiments on3new-type long columns and3new-type short columns. Besides,1conventional long column and2conventional short columns were used in the contrast test.The result demonstrated that steel-concrete composite joints significantly improved thebending deformation capacity of columns. When steel-concrete composite joints were slide,the shearing deformation capacity of columns was greatly enhanced. All damages ofnew-type long columns were constrained in steel-concrete composite joints, showing the steelbar yield and fracture. The concrete of the column body expect steel-concrete composite joints did not show any damage. Meanwhile, once the concrete of conventional columns iscrushed, the stability of axial force cannot be maintained and the conventional columns willsoon lose carrying capacity. The deformation capacity of new-type long columns can exceedthat of conventional long column by2to5times. The deformation capacity ofnew-type shortcolumn can exceed that of conventional short column by about1.6to2.0times. Experimentaldata and numerical analysis presented that new-type columns may slide and produce theeffects of friction energy.To verify the practical effect of new-type frame structure, this paper carried out acomparative experiment with1new-type frame and1conventional frame. The experimentalresults demonstrated that the damaged area of frame column (long column) was located at thesteel-concrete composite joint of column ends. The concrete of column body did not crack,and the axial force can always be stabilized. After the damage of pull rod, the frame keptworking until the crack of steel-concrete composite joint steel. The destruction area ofconventional frame focused on the column end. When the concrete of column end wascrushed, the stirrup fell off in an outward way. The longitudinal reinforcement was bent andbulged. After reaching the peak bearing capacity, the stable axial force cannot be maintainedand the horizontal force dropped quickly. The yield displacement and peak displacement ofnew-type frame was2.71and2.0times of conventional frame. The peak displacement anglewas larger than1/50, which is1.49times of the specifications. Yield capacity and peakcarrying capacity was more than3times than that of the conventional frame, and the elasticintersection angle rigidity was1.55times than that of conventional frame. With the sameloading system, the times of loading cycle of the new-type frame were greater thanconventional frame, and the energy dissipation capacity was much more superior thanconventional frame, showing excellent seismic performance.To understand the repairability of the new-type structure, this paper also repaired thedamaged new-type frame and new-type column. The same experimental equipment wereused and the experiment was repeated with the same loading system. The result demonstratedthat the repairing of new-type frame structure and new-type column was simple and fast.Besides, the cost was low. After repairing, the new-type frame structure and new-type columncan be applied into practices, and eliminate most of the residual deformations made by the original destruction. Compared with the original structure, performance indicators did notvary remarkably, indicating that the new-type structure had superior repairability.This research adopted the numerical analysis method to examine the impact of differentjoint parameters on the mechanical properties of new-type columns. The unit rigidityequation of new-typeframe column and prestressed tie rod was derived. This solved theoverall analysis of the new-type structure. Besides, this paper also deduced a designing andcalculating method of compression-bending capacity of composite steel-concrete joints.Moreover, the research aslo reached the mechanical conditions of friction sliding energydissipation produced by steel-concrete composite joints. This can provide theoretical supportsfor the promotion and application of the new-type structure.Steel-concrete composite joints have remarkable deformation capacity, which canprotect the concrete of column body. This is equivalent to the effects of specified “strongcolumn-weak beam”. As long as the concrete-filled steel tubes of steel-concrete compositejoints remain intact, the new-type structure can maintain the stability of axial force and theshear-bearing capacity of column end. This presents remarkable significance to the seismicfortification target of No Collapsing in the Strong Earthquake. The repairing of the new-typestructure is simple and fast with low cost. There is no need of technical clearance time, thussuitable for quick repair after the earthquake. Therefore, it shows practical meanings.