Concentrated load on structural slab
Concentrated load on structural slab
(OP)
Can anyone give me the ACI Code requirement for the maximum width of one way slab which can be considered effective in resisting a concentrated load? Thanks.
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Concentrated load on structural slab
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RE: Concentrated load on structural slab
RE: Concentrated load on structural slab
Westergaard, a professor at the University of Illinois, issued a comprehensive report in March of 1930 to the Bureau of Public Roads "Computation of Stresses in Bridge Slabs due to Wheel Loads". I believe Westergaard's report is the basis for the modern day AASTHO requirements. The AASTHO spec., unfortunately, has taken Westergaard's recommendations and converted them into engineering data that works only for truck loads and bridges. Building engineers must work with varying wheel bases, axle lengths and tire contact areas. You must go back to Westegaard's original report to find useful information. You should be able to order this report thru your Public Library.
This report has charts that give coefficients both for principal and distribution reinforcements for one way slabs subjected to concentrated loads. It has charts to handle overlapping stresses, when wheel loads are parallel or perpendicular to the span. It even takes into account the contact area of the concentrated loads.
I hope this helps!
RE: Concentrated load on structural slab
Sometimes what I do is find out the actual bearing area of the concentrated load (say it is distributed uniformly over a 2ft by 2ft area). Treat the width of the loaded area as the width of a "beam" element within the slab (but the "beam" depth is the same thickness as the slab of course!)
Then you calculate the effective overhanging flange width on either side of the width of the loaded area.
The total effective width in each direction is the width of the loaded area plus the width of the effective slab overhang. This is what I use for the effective resisting width of point loads.
RE: Concentrated load on structural slab
The amount of reinforcement, placed at right angles to the main reinforcement (often called distribution steel), is very important and is generally more than the normal requirement for temperature and shrinkage steel. This steel is what helps the concentrated load(s) spread out over the effective width.
RE: Concentrated load on structural slab
http://www.mathcad.com/Library/DisplayCategory.asp?c=40...
RE: Concentrated load on structural slab
Sorry, but the MathCad file is for a slab on grade.
RE: Concentrated load on structural slab
b_ef = b_load + 2.4*a*(1.0 – a/L_n)
where:
- ‘b_ef’ is the effective width
- ‘b_load’ is the load width
- ‘a’ is the perpendicular distance from the nearer support to the section under consideration
- ‘L_n’ is the length of clear span
As ‘b_load’ approaches 0 and ‘a’ approaches L_n/2, ‘b_ef’ approaches 60% of L_n.
RE: Concentrated load on structural slab
RE: Concentrated load on structural slab
RE: Concentrated load on structural slab
RE: Concentrated load on structural slab
EffWidth=
actual width of load
+0.6·(span - dimension of load parallel to span)
RE: Concentrated load on structural slab
The design of flexural reinforcement is based on a rectangular stress block with a uniform compressive stress of 0.85*f_c (where f_c is the characteristic compressive cylinder strength of concrete at 28 days) and a maximum strain in the extreme compressive fibre of 0.003.
Cross-sectional steel area is calculated from the following equation for the moment capacity (kNm/m):
phi*m_u = (phi*f_c*q*(1 – q/1.7)*d^2)/1000 [kNm/m]
where:
- phi: strength reduction factor, equal to 0.8 for slabs [dimensionless]
- m_u: ultimate moment capacity [kNm/m]
- f_c: characteristic compressive cylinder strength of concrete at 28 days [MPa]
- q = (A_st*f_sy)/(1000*d*f_c)
where:
- A_st: cross-sectional area of tension reinforcement [mm^2]
- f_sy: yield strength of reinforcing steel [MPa]
- d: effective depth of a cross-section, i.e. the distance fro extreme compressive fibre to the resultant tensile force in the reinforcing steel [mm]
RE: Concentrated load on structural slab
RE: Concentrated load on structural slab
Good luck.