RAFT FOUNDATION DESIGN (BS8110 : Part 1 : 1997) TEDDS calculation version 1.0.02; Library item - Raft title Soil and raft definition Soil definition Allowable bearing pressure; qallow = 50.0 kN/m2 Number of types of soil forming sub-soil; Two or more types Soil density; Firm Depth of hardcore beneath slab; hhcoreslab = 150 mm; (Dispersal allowed for bearing pressure check) Depth of hardcore beneath thickenings; hhcorethick = 250 mm; (Dispersal allowed for bearing pressure check) Density of hardcore; hcore = 19.0 kN/m3 Basic assumed diameter of local depression; depbasic = 2500mm Diameter under slab modified for hardcore; depslab = depbasic - hhcoreslab = 2350 mm Diameter under thickenings modified for hardcore; depthick = depbasic - hhcorethick = 2250 mm Raft slab definition Max dimension/max dimension between joints; lmax = 10.000 m Slab thickness; hslab = 250 mm Concrete strength; fcu = 40 N/mm2 Poissons ratio of concrete; = 0.2 Slab mesh reinforcement strength; fyslab = 500 N/mm2 Partial safety factor for steel reinforcement; s = 1.15 From C&CA document ‘Concrete ground floors’ Table 5 Minimum mesh required in top for shrinkage; A142; Actual mesh provided in top; A393 (Asslabtop = 393 mm2/m) Mesh provided in bottom; A393 (Asslabbtm = 393 mm2/m) Top mesh bar diameter; slabtop = 10 mm Bottom mesh bar diameter; slabbtm = 10 mm Cover to top reinforcement; ctop = 50 mm Cover to bottom reinforcement; cbtm = 75 mm Average effective depth of top reinforcement; dtslabav = hslab - ctop - slabtop = 190 mm Average effective depth of bottom reinforcement; dbslabav = hslab - cbtm - slabbtm = 165 mm Overall average effective depth; dslabav = (dtslabav + dbslabav)/2 = 178 mm Minimum effective depth of top reinforcement; dtslabmin = dtslabav - slabtop/2 = 185 mm Minimum effective depth of bottom reinforcement; dbslabmin = dbslabav - slabbtm/2 = 160 mm Edge beam definition Overall depth; hedge = 500 mm Width; bedge = 500 mm Angle of chamfer to horizontal; edge = 60 deg Strength of main bar reinforcement; fy = 500 N/mm2 Strength of link reinforcement; fys = 500 N/mm2 Reinforcement provided in top; 2 T20 bars (Asedgetop = 628 mm2) Reinforcement provided in bottom; 2 T20 bars (Asedgebtm = 628 mm2) Link reinforcement provided; 2 T10 legs at 250 ctrs (Asv/sv = 0.628 mm) Bottom cover to links; cbeam = 35 mm Effective depth of top reinforcement; dedgetop = hedge - ctop - slabtop -edgelink - edgetop/2 = 420 mm Effective depth of bottom reinforcement; dedgebtm = hedge - cbeam - edgelink - edgebtm/2 = 445 mm Internal slab design checks Basic loading Slab self weight; wslab = 24 kN/m3 hslab = 6.0 kN/m2 Hardcore; whcoreslab = hcore hhcoreslab = 2.9 kN/m2 Applied loading Uniformly distributed dead load; wDudl = 0.0 kN/m2 Uniformly distributed live load; wLudl = 0.0 kN/m2 Slab load number 1 Load type; Point load Dead load; wD1 = 0.0 kN Live load; wL1 = 75.0 kN Ultimate load; wult1 = 1.4 wD1 + 1.6 wL1 = 120.0 kN Load dimension 1; b11 = 440 mm Load dimension 2; b21 = 440 mm Internal slab bearing pressure check Total uniform load at formation level; wudl = wslab + whcoreslab + wDudl + wLudl = 8.9 kN/m2 Bearing pressure beneath load number 1 Net bearing pressure available to resist point load; qnet = qallow - wudl = 41.2 kN/m2 Net ‘ultimate’ bearing pressure available; qnetult = qnet wult1/(wD1 + wL1) = 65.8 kN/m2 Loaded area required at formation; Areq1 = wult1/qnetult = 1.823 m2 Length of cantilever projection at formation; p1 = max(0 m, [-(b11+b21) + ((b11+b21)2 - 4(b11b21 - Areq1))]/4) p1 = 0.455 m Length of cantilever projection at u/side slab; peff1 = max(0 m, p1 - hhcoreslab tan(30)) = 0.368 m Effective loaded area at u/side slab; Aeff1 = (b11 + 2 peff1) (b21 + 2 peff1) = 1.385 m2 Effective net ult bearing pressure at u/side slab; qnetulteff = qnetult Areq1/Aeff1 = 86.6 kN/m2 Cantilever bending moment; Mcant1 = qnetulteff peff12/2 = 5.9 kNm/m Reinforcement required in bottom Maximum cantilever moment; Mcantmax = 5.9 kNm/m K factor; Kslabbp = Mcantmax/(fcu dbslabmin2) = 0.006 Lever arm; zslabbp = dbslabmin min(0.95, 0.5 + (0.25 - Kslabbp/0.9)) = 152.0 mm Area of steel required; Asslabbpreq = Mcantmax/((1.0/s) fyslab zslabbp) = 89 mm2/m PASS - Asslabbpreq
Posted on: Sun, 21 Jul 2013 11:07:55 +0000
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