Hello
I have designed a number of small thin-slabs to BS8110. The slabs are simply-supported on all four sides, are 100-mm thick, 1000-mm wide and range from 1000-mm long to 5500-mm long. There is no provision for torsion-steel and there is no 'uplift' restraint at the edges. The slabs are hollow and ribbed with the ribs at 150-mm centres and a single rebar.
I designed the slabs using equations 10 and 12 for the bending-resistance and Table 3.15 for shear resistance.
During my analysis, I came to the slabs with span:length ratios in excess of 1:2 and found some problems. With respect to the bending-resistance. I have always been led to believe that a slab ceases to be two-way spanning when ratios exceed 1:2. I have searched BS8110 for one-way:two-way cut-off and the only reference appears in Tables 3.13 where the span:length ratio cut-off is 2.0. Using the equations 10 and 12, I have confirmed all the values in Table 3.13. For a 1-m wide slab supporting a 1-unit load, the one-way bending moment is 0.125; the two-way bending-moment is 0.118. I evaluated other values using the equations and a two-way slab moment becomes equal to the one-way moment at a ratio of 1:4. Beyond 1:4, it matters not whether I use the two equations or FL/8. I have searched a few text books and the only 1:2 proof has been commentary only. Therefore, the 1:2 ratio is arbitrary and slabs act two-way up to ratios of 1:4 and one-way beyond.
For the shear-resistance, vx < vc so shear-steel not required but I am unable to find a suitable equation or table to replace Table 3.15. The table refers to slabs with torsion-resistance (mine do not) and the cut-off ratio for the slab is 1:2. I'm not sure that I should be using this table but cannot find a simply supported equivalent with no torsion steel or an equation that derives the table.
Basically, I am a bit lost on how to proceed with the shear-resistance of a thin slab with no torsion-steel up to ratios of 1:2 and beyond.
Any advice very, very much appreciated.
I have designed a number of small thin-slabs to BS8110. The slabs are simply-supported on all four sides, are 100-mm thick, 1000-mm wide and range from 1000-mm long to 5500-mm long. There is no provision for torsion-steel and there is no 'uplift' restraint at the edges. The slabs are hollow and ribbed with the ribs at 150-mm centres and a single rebar.
I designed the slabs using equations 10 and 12 for the bending-resistance and Table 3.15 for shear resistance.
During my analysis, I came to the slabs with span:length ratios in excess of 1:2 and found some problems. With respect to the bending-resistance. I have always been led to believe that a slab ceases to be two-way spanning when ratios exceed 1:2. I have searched BS8110 for one-way:two-way cut-off and the only reference appears in Tables 3.13 where the span:length ratio cut-off is 2.0. Using the equations 10 and 12, I have confirmed all the values in Table 3.13. For a 1-m wide slab supporting a 1-unit load, the one-way bending moment is 0.125; the two-way bending-moment is 0.118. I evaluated other values using the equations and a two-way slab moment becomes equal to the one-way moment at a ratio of 1:4. Beyond 1:4, it matters not whether I use the two equations or FL/8. I have searched a few text books and the only 1:2 proof has been commentary only. Therefore, the 1:2 ratio is arbitrary and slabs act two-way up to ratios of 1:4 and one-way beyond.
For the shear-resistance, vx < vc so shear-steel not required but I am unable to find a suitable equation or table to replace Table 3.15. The table refers to slabs with torsion-resistance (mine do not) and the cut-off ratio for the slab is 1:2. I'm not sure that I should be using this table but cannot find a simply supported equivalent with no torsion steel or an equation that derives the table.
Basically, I am a bit lost on how to proceed with the shear-resistance of a thin slab with no torsion-steel up to ratios of 1:2 and beyond.
Any advice very, very much appreciated.
