Presentation on theme: "Design Of Foundation for a Commercial and Residential Building"— Presentation transcript:
1Design Of Foundation for a Commercial and Residential Building An-Najah National UniversityEngineering CollageCivil Engineering DepartmentDesign Of Foundation for a Commercial and Residential BuildingUnder the Supervision of:Dr. Mohammad GhazalPrepared by:Moayad QadarahRaja’e OmarLu’ai Abu SharshuhMay 2011
2Project Description Name: Eisheh Taha Oudeh Building. Type: commercial and Residential Building.Location: Nablus City, Rafedia Main Street, opposite to Ben Qutaiba School.Number Of Floors: 12 floor, 2 under ground level and 10 over.Plane Area: 550 m2 for the floor.
3SCOPE OF PROJECT Evaluation of foundations. Selection of the proper foundations.Design of foundations.
4Literature ReviewFoundations are the part of an engineered system to receive & transmit loads from superstructure to the underlying soil or rock .There are two types of foundations : shallow & deep foundations.Many factors should be taken into consideration in choosing foundation types such as soil properties , economic factors, engineering practice, ....etc
5Types of footing Isolated Footing. Combined Footing. Mat or Raft Foundations.Strap or Cantilever Footings.Pile Foundations.
6 Isolated Footings Are used to support single columns. This is one of the most economical types of footings and is used when columns are spaced at relatively long distances.Its function is to spread the column load to the soil , so that the stress intensity is reduced .
7Combined Foundations Are used in the following cases: 1) When there are two columns so close to each other & in turn the two isolated footing areas would overlap.2) When the combined stresses are more than the allowable bearing capacity of the soil.3) When columns are placed at the property line.
8Mat or Raft Foundations Are used to spread the load from a structure over a large area, normally the entire are of the structure .They often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.They have the advantage of reducing differential settlements.
9Strap or Cantilever Footings Cantilever footing construction uses a strap beam to connect an eccentrically loaded column foundation to the foundation of an interior column .Are used when the allowable soil bearing capacity is high, and the distances between the columns are large .
10Pile FoundationsThey are long & slender members that are used to carry & transfer the load of the structure to deeper soil or rocks of high bearing capacity, when the upper soil layer are too weak to support the loads from the structure.Piles costs more than shallow foundations; so the geotechnical engineer should know in depth the properties & conditions of the soil to decide whether piles are needed or not.
11Bearing CapacityBearing Capacity : is the ability of a soil to support the loads applied to the ground .Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure;Allowable bearing capacity is the ultimate bearing capacity qu divided by a factor of safety (F.S).There are three modes of failure that limit bearing capacity: general shear failure, local shear failure, and punching shear failure.
12SettlementWhen building structures on top of soils, one needs to have some knowledge of how settlement occurs & how fast settlement will occur in a given situation.So, There are three types of settlement:1. Initial settlement2. Primary settlement3. Secondary settlement
13Settlement (Cont.) Total Settlement = SI + SC + SS The allowable bearing capacity and the type of foundations provided later are evaluated based on the settlements limits. This means that the settlement of the proposed foundation would be within the acceptable limits if the allowable bearing capacity provided is used.
14Geotechnical Investigation The studied area is approximately flat with slight difference in the three existing elevations. The general soil formation within Highly fragmented weathered limestone and marlstone of soft to medium strength with cavities filled with marl soilThe geotechnical engineer decided to drill Three boreholes trying to cover the whole construction area.
16The depths of the drilled boreholes were as follows: Borehole No.Depth (m)116.0210.03laboratory test results:γ= 20 KN/m³qall. = 3.5 kg/cm2
17Taking the lowest compressive strength value of rock core specimens with test results and applying the percentage of 5%, the strength will be:b.h1 – Qall = 5% * 75 = 3.75 kg\cm2b.h2 – Qall = 5% * 70 = 3.5 kg\cm2b.h3 – Qall = 5% * 78 = 3.9 kg\cm2But considering the fact that rocks is some areas may be encountered in fragmented conditions, as well as the presence of there fracture rocks and marls, it is recommended to consider the bearing capacity value of the rock formations countered in the site of not more than 3.5 kg\cm2 within the described rock layers after the removal of all loose fill materials over the rock.
18Structural designColumn loads are calculated using (sap program), the structure subjected to the following loads:1) Dead Load (own weight).2) Super imposed dead load =350 kg/m2.3) Live load =500 kg/m2.Using ACI code, the ultimate loads are calculated consideringload combination :Pu =1.2Dead + 1.6Live.Material characteristics used in this project are:f’c =240kg/cm2 (B 300)Where:f’c is the compressive strength of concretefy = 4200 kg/cm2fy is the yield strength of steel
19Isolated Footing Design Manual Design steps:Area of footing = Total service loads on column / net soil pressureDetermine footing dimensions B & H .Assume depth for footing.Check soil pressure.Check wide beam shear : Vc > VultCheck punching shear : Vcp > Pult, punchingDetermine reinforcement steel in the two directions.Check development length .
20DIMENSIONS OF SINGLE FOOTING Area (m2 )L(m)B(m)Footingcolumn126.96.36.199F1c1F2c22.521.4F3c31.7F4c4F5c52.231.651.35F6c620.254.5F15C1514.764.13.6F16c16184F19c19188.8.131.52F20c20102.5F28c28F31c3184.108.40.206F34c3410.53F35c357.022.6F36C36
21THICKNESSES OF FOOTINGS Depth of footing will be controlled by wide beam shear (one way action) and punching shear (two way action).Wide Beam Shear:Shear cracks are form at distance “d” from the face of column,and extend to the compression zone, the compression zone will be fails due to combination of compression and shear stress.Punching Shear:Formation of inclined cracks around the perimeter of the concentrated load may cause failure of footing.Max, formation of these cracks occurred at distance “d\2” from each face of he column.
22THICKNESSES OF SINGLE FOOTINGS h(m)d(m)Footingcolumn0.40.32F1c10.3F2c2F3c3F4c4F5c5F6c610.9F15C15F16c16F19c19F20c20F28c28F31c310.80.7F34c34F35c350.60.5F36C36
23Steel reinforcement :Isolated footing represented as cantilever, so the max moment occurs at the face of the column:Ultimate moment at the face of the column(Mult) =(qult*ln2)/2Mn =Mu\Φ , where, Φ=0.9Mn =Rnbd2ρ = 1\m(1-( 1-2mRn\ fy ).5)WHEREρ: Steel ratiom= fy\0.85 f′cAs = ρbd
24single footing reinforcement: Reinforcement in long direction/cmReinforcement in short direction/cmFooting1ø16/271ø14/21F11ø16/281ø14/20F2F3F41ø14/27F5F61ø18/121ø18/10F15F161ø18/13F191ø16/11F20F28F311ø16/121ø14/10F34F351ø14/12F36
25DESIGN OF COMBINED FOOTING columnFc1C7,C8Fc4C23,C24Fc5C26,C27Fc6C29,C30Fc7C32,C33SUMMARY OF DIMENSIONSh(m)d(m)L(m)B(m)Footing.220.127.116.11Fc111.5Fc21.51.464.5Fc372Fc4Fc593Fc6Fc7
26Steel Reinforcement (Flexural) By using sap program to get the maximum negative and positive MomentMn =Mu\Φ , where, Φ=0.9Mn =Rnbd2As = ρbdSteel reinforcement for Fc2The figure below show bending moment in x-direction using SAP2000:
27The figure below show bending moment in y-direction using SAP2000: Mu =93.175ton.mMn =93.175\.9=103.52ton.mMn =Rnbd2Rn =21.1kg\cm2Ρ =.0054As =37.8cm2Use 1 Φ16\12cmThe figure below show bending moment in y-direction using SAP2000:
28Steel reinforcement for Fc2 Mu = ton.mMn = / 0.9ton .mMn =Rnbd2Rn=20.1kg\cm2Ρ=.005As =37.5cm2Use 1 Φ16\12cm
29Steel reinforcement for Combined footing Reinforcement in y directionReinforcement in x directionFooting #1Ф16/12cmFc 11Ф18/10cm1Ф22/10cmFc2Fc 31Ф32/10cmFc 4Fc 5
30Calculating the Thickness for mat Mat foundation DesignIn this project the mat foundation was designed using Sap2000 with the following data: ( fc= 240 kg \cm2,fy= 4200 kg\cm2 )Calculating the Thickness for matThe thickness of mat foundation was calculated using check for punching in the next calculation .(the most critical for determining the thickness for mat in the punching shear )To calculate the thickness , it was used the next equation:Pu = .75*1.06(fc).5 *bo*d
31Pu : the load at the column bo: parameter of the bunching area Where :Pu : the load at the columnbo: parameter of the bunching aread: thickness of the mat foundationfor mat foundation 1which include (col 21,22,25)Col 21 has the critical load,Pu = ton377.29*1000 = .75*1.06*(240).5*(2(d+50)+(2(d+70))*dd = 80 cm
32Design of mat foundation using sap 2000 Deflection shapeWhen we do the analysis using sap 2000 it was found that the maximum settlement was equal to m
33Reinforcement reinforcement in x direction we take the maximum moment at the face of columnsand the maximum between the columns.Then ,the area of reinforcement will calculate by theEquation:As =p*b*d1)at the face of columnMu =123 ton .mp=As = *100*80As = 43 cm2 use 10Ф25 mm/m2)between the columnsMu = 40 ton.mP =0.0016˂0.0033So use pmin = 0.003As=26.4 cm2 use 10Ф18 mm/m
34reinforcement in y direction 1)at the face of columnMu = 75 ton.mρ= ˂use ρ min for all the zone.As = ρ * b * d = * 100 * 80= 26.4 cm2Use 10 Ф 18 mm / msecondary reinforcement (Negative moment)the max. moment equals to 20 ton.mΡ = ˂