by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : December 2008
TECHNICAL the strut’s capacity. The parameters that have been investigated are the strength of the concrete, span-to-depth ratio, lateral confi nement and the width and extent of cracks and their orientation to the strut due to transverse tensile strains. For this analysis the nomenclature adopted for the design compression strength are shown in Equations (1) and (2): fvf ¢¢c cd = f c ¢ = The effective compressive strength v = The strut effi ciency factor that is = 1 The design compressive strength is: ff cd =F ¢cd (2) (1) vfc./200¢ =- 0 8 (3) effi ciency factor is determined by equating the areas between the rigid-plastic and the actual stress-strain curve to the point of ultimate strain. It was shown by Foster and Gilbert (1996) that AS36002 This is based upon the study by Nielsen et al (1978) that reviewed how plain concrete strain softens and is brittle under compression. This is idealised as a rigid-plastic model (fi gure 1) that shows a yield plateau that acts at sc = vf’c has a poor correlation against experimental data and significantly underestimated the strength of the strut. European Code – CEB FIP The European Code, CEB FIP (1990)5 vfc./250¢ 0()6 1 vfc./250¢ =- =- 0 ()85 1 , also uses this form of the equation though it differentiates between cracked and uncracked struts. for uncracked for cracked (4) (5) This code identifi es the effect of cracking due to transverse tensile stresses. However it does not take into account the degree of cracking. It should be noted that cracks may have also formed from a different load case and affect the design. Canadian Code – CSA A23.3 The Canadian Code, CSA A23.33 Figure 1. Rigid-Plastic Idealisation (Carino and Duthinh 1996). Australian Code – AS3600 The current Australian Code, AS36002 the concrete strength. , is based on extensive panel , uses a single parameter, tests undertaken by Vecchio and Collins (1986) of normal strength concrete in the range of 12 to 35 MPa. Vecchio and Collins (1986) showed that the maximum compression strength can be signifi cantly reduced when there are transverse tensile strains present. From this Collins and Mitchell (1986) developed an efficiency . The Figure 2. Code Comparison of the Design Compressive Strength of a Strut. StrutAngle (degrees) 50 Concrete in Australia Vol 34 No 4 f cd ¢ / f c ¢