Experimental Study On Mechanical Performance And Design Method Of Steel Reinforced Lightweight Aggregate Concrete Beams

Composed of lightweight aggregate concrete and structural steel, SRLC (Steel reinforced lightweight aggregate concrete) structures have both merits of SRC (Steel reinforced concrete) structures such as high strength, large stiffness and good ductility etc., and some additional merits such as lighter deadweight, less response under earthquake and better durability etc. SRLC structures can give us a new way to widen the applying range of SRC structures.Based on the analysis of the existing experimental results and the changes of the pertinent regulations related to the concerning standards, the conversion relations between axial compressive strength or direct tensile strength and cubic compressive strength of lightweight aggregate concrete were deduced; statistic parameters for the strength of lightweight aggregate concrete were obtained by using statistic analysis method; the characteristic value of axial compressive strength and direct tensile strength of lightweight aggregate concrete were acquired. Stress-strain curve of lightweight aggregate concrete and equivalent rectangular stress block coefficients related to the bending capacity of the normal section were also put forward.Eight reinforced high-strength concrete beams (six were made of lightweight aggregate concrete and two were made of normal density concrete) were tested to study the carrying capacity of normal section; calculation method of carrying capacity of normal section on lightweight aggregate concrete beams was put forward. Calculation method of flexural stiffness, deflection and crack width of high-strength lightweight aggregate reinforced concrete beams was put forward. Based on the experimental data of shear capacity of inclined section of 110 lightweight aggregate concrete beams, the calculation formula of shear capacity of lightweight aggregate concrete beams was put forward by reliability analysis, according to the demand of Unified Standard for Reliability Design of Building Structures (GB50068-2001). During the procedure, the second moment of first order method recommended in the National Design Standard of Building Structures (GBJ68-84) was applied.According to the conditions used to determine the minimum steel ratio and research achievements of lightweight aggregate concrete structures, calculation formulae of minimum steel ratio under shear and torsion were derived.Eight SRLC beams and two SRC beams under bending were tested; full procedure and damage form and behavior were observed. It was showed that: The behavior of SRLC beams under bending was familiar to that of SRC beams, and there was no significant turning point on the load-deflection curve—which means that cracking of concrete located in the tensile range has little effect on the total flexural stiffness. Yield point of the beam was marked by the yielding of the tensile flange of the steel beam. Before yielding, strain distribution along the height of the beam section approximately shaped as a line. But after yielding, the "line" didn't exit caused by the slip between the steel beam and concrete, which leaded to a larger deflection. After passing the limit point these beams still had considerable carrying capacity and showed good ductility. The calculation method of carry capacity of the normal section were derived, as much as the calculation method and calculation formulae of stiffness and crack width.Fifteen SRLC beams and two SRC beams under shear force were tested which showed that the behavior of SRLC beams under shear force was familiar to that of SRC beams: Ifλ(shear span ratio)≤1.5, oblique compression damage occurred; if 1.5≤λ≤1.5, shear-compression damage occurred; ifλ≤3.0, bending damage or shear-bending damage occurred. The calculation formulae of carry capacity of the oblique section under shear was derived.FEM (finite element method) has been used to determine the load-defection curve, and the load and related deflection at the crack point, at the yielding point and at the limit point. The damage mode, the procedure of deflection development and design factors related to the behavior of the beam such as dimension,λand concrete strength etc. were also observed. The calculated results have a good agreement with that of test, which shows that the program given by this dissertation is reliable.