Experimental Study On The Effects Of Axial Compress Ratio To Double-span Prestressed Concrete Frame

The technique of prestressed concrete is already to get in our civil engineeringrealm more and more extensive application. For the statically indeterminate structure ofprestressed concrete,it is especially have the favor of the designers by its superiority.These year, internal and foreign specialists in the prestressed concrete field dedicatethemselves into the study on statically indeterminate structures of prestressed concreteand get some cognitions of their mechanice characteristics and specialities of internalforce redistribution. These study results offer the engineering realm good references.Because of the characteristics of itself, prestressed concrete structures are often used tobottom wide bays or transform-floors. For these structures, the span of frame beamsincrease, the load-supported areas of single column increase,the number of upside-layesis more, So the axial compress ratio of frames is relatively big and it is necessary for usto consider its effect to moment redistribution. But most references in existence onlyconsider the effects of axial compress ratio to structure ductility and donot discuss theeffects of axial compress ratio to structure internal forces and internal forcesredistribution. With the impersonal and precise attitude, the civil engineering college ofchongqing university has finished the experimentation of two full-scale. One layer anddouble-span prestressed concrete frames. In allusion to the two prestressed frames of different axial compress ratiosupporting non-symmetrical loads, this paper discusses crack develop-rules andstructural plastic moment redistributions of the loading process. The main conclusionsof the paper are below: (1) For single-span and double-span prestrssed frames, the second-order effectbrought by the change of axial compress ratio always effects structural internal forces,but the effect extent is only about 1% at the column-bottom sections which are effectedmost markediy. So it can be ignored. (2) For the frames of which only partial frame-columns exist axial compress ratioor which the axial deformations of frame columns are different, changes of axialcompress ratio will bring changes of structural internal forces, and the changes will bemore obvions with the decreases of the ratio of beam rigidity to column. When axialcompress ratio increases to a certain degree, the column-bottom moment of the span ofside-column which exists axial compress ratio will exceed the moment of the IIcorresponding beam-border's bearing, the structures maybe destroy at the form ofcolumn-hinge mechanismfinally. (3) For prestressed frames, the change of axial compress ratio will effect theductility of frame column. To realize the aim of "experted rare earthquakes, nocollapse", it is necessary to regulate the limit axial compress ratio of prestressedconcrete frame column which is not a fixed value but should be adjusted by realconditions. (4) axial compress ratio effects the limit loads of prestressed frames so little thatwe can conclude axial compress ratio effects only the internal force redistribution butnot the last moment mondulation results of prestressed concrete frames.