RC Frame-shear Wall Structures With Partial Columns Sliding At Upper Ends

Columns are the primary load-carrying components of reinforced concrete (RC)frame-shear wall structure. Serious damages to columns under strong earthquake are likely tolead to a partial or full collapse of the whole structure. If the load-carrying components andthe shearing forces on partial columns can be greatly reduced by special constructionalmeasures, they could be nearly intact under strong earthquake. In the case that they are giventhe load capacity of the weight of all the structure at the design stage, it is ensured that thestructure will not collapse under strong earthquake. Based on this idea, we propose theconcept of RC frame-shear wall structures with partial columns sliding at upper ends (FSPCS).Upper ends of partial columns (sliding columns) of FSPCS are separated with their adjacentjoints, and some sliding materials are set up between them, but the lower ends of thesecolumns are fixed with adjacent beams and slabs. If the friction coefficient of the slidingmaterials is very small, the sliding columns are subjected to axial force mainly but nearly nobending moment and shear force. This paper performs a preliminary study on designprocedures, seismic performance, P-δ effect and torsion effect of FSPCS through theoreticalanalysis, numerical simulation and model test. The main research work and conclusions are asfollows:1. The design procedures of FSPCS are suggested, and its construction costs andElastic-plastic earthquake responses are compared with conventional frame-shear wallstructures. Simulation results show that:(a) the friction support located at upper end of thesliding column under minor earthquake can be approximately treated as a joint;(b) the slidingat upper ends of columns significantly reducing the bending moment and shear force of partialcolumns, the collapse-resistant capacity of FSPCS can be better than that of the conventionalstructures with a slight increase in construction cost;(c) in the case that the frictioncoefficients at the upper ends of partial sliding columns are in a certain range, the lateralstiffness of FSPCS is not only similar to that of the conventional structures to prevent FSPCSfrom damage under minor earthquake, the vertical load bearing capacities of FSPCS can alsobe maintained to prevent FSPCS from collapse when subjected to major earthquake.2. Studies on FSPCS are carried out in great depth through a mix of theory and exampleanalysis, which covers design of the frame beams, assessment of the lower limit value offriction coefficient, and energy dissipation analysis of the friction supports. Simulation resultsshow that:(a) by taking the hardening of tensile reinforcements into account and adjusting thedesign procedures, the frame beams may be designed more economically;(b) the assessment method for the low limit value of friction coefficient is closely related to current design code,making it easier for engineers’ application;(c) a larger additional damping ratio can beprovided by the friction supports under moderate earthquake, which leads to considerableenergy-dissipated effect.3. Comparative shaking table tests are conducted for a RC structural model with partialcolumns sliding at upper ends (Model B) and an ordinary RC structural model (Model A). Inaddition, mechanical performances of two friction supports are tested to determine the rangeof the friction coefficient. Test results show that:(a) the average value of the frictioncoefficient for friction supports composed of Teflon and stainless steel mirror plate withoutlubrication oil is about0.070~0.095, while that with lubrication oil is about0.014~0.018;(b)the maximum interstory drift ratios related to the weak story, the maximum relativedisplacements related to the top story, the maximum absolute accelerations related to the weakstory, and the maximum absolute accelerations related to the top story for Model B underearthquakes with different peak ground accelerations are, respectively,20%～43%,17%～32%,12%～22%, and7%～33%less than those for Model A; and (c) the maximuminterstory shear forces related to each floor of Model B are all less than those of Model A.Generally, the seismic performances of FSPCS are better than those of the ordinary RCframe-shear wall structures.4. The characteristics of the second-order moment of the sliding column withoutsideway due to the P-δ effect are investigated for different cases, the boundary condition isgiven for considering the secondary moment, and a method is proposed to determine theincrement coefficient of bending moment for the sliding column without sideway; finally theconcrete nonlinearity is taken into account primarily by amending the parameters in theproposed method, and numerical examples are given. It is found that:(a) in the case thatβcr<β<π, the second-order moment of the sliding column without sideway due to the P-δeffect increases the maximum bending moment in the column; and (b) in the case that βcr<β<π,the maximum bending moment can be easily determined by using the first-order moment ofthe sliding column without sideway and the aforementioned increment coefficient.5. Seismic torsion response of FSPCS due to accidental eccentricity is revealed, so is theinfluence law of structural period ratio and length-width ratio on such a response. It’scompared to conventional frame-shear wall structure, and the corresponding designsuggestions are proposed. It can be found that:(a) accidental eccentricity taken into account,the elastic torsion response of FSPCS is less than that of conventional frame-shear wall structure, and the influence law of structural period ratio and length-width ratio on the formeris almost the same as the latter;(2) as the structural period ratio increases, the wholeincrement of the maximum horizontal displacement of top storey of FSPCS under majorearthquake is on a rising trend, but it’s always less than that of conventional frame-shear wallstructure, and the rise is less than that under minor earthquake;(3) as the structural length-width ratio increases, the increment of the maximum horizontal displacement of top storey ofFSPCS under major earthquake is on a trend of first increase and then decrease. The increaseis significant as the length-width ratio changes from1to2.