Those flat roof which face a problem of water accumulation require stability analysis under ponding conditions. For checking the stability we need to see the following equations, if both of these are fulfilled
Cp+0.9Cs<= 0.25
Id>=25S4/106
Where
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We take the smaller value out of these two conditions to calculate the total horizontal shear which is to be to be resisted by the shear connectors in building construction
Vh= 0.85f‘cAc/2
Vh=As Fy/2
where
Vh = Total horizontal shear, kip (kN), between maximum positive moment and each end of steel beams (or between point of maximum positive moment and point of contraflexure in continuous beam)
f‘c= Specified compressive strength of concrete at 28 days, ksi (MPa)
Ac = Actual area of effective concrete flange in inch2(mm2)
As = Area of steel beam in inch2(mm2)
Total number of connectors required to resist Vh is given by Vh/q
where q is the allowable shear for one connector, kip (kN) and its value is given in structural design guides.
Some keypoints should be considered
1. Required number of shear connectors should be placed uniformly in the section having zero to maximum moment.
2. Shear Connectors should have a minimum of 25.4mm (1inch) of concrete cover in all the directions.
3) Stud diameter should not exceed 2.5 times the beam-flange thickness. ( May increase only if studs are located directly over the web)
In a composite construction, a concrete slab and steel beams act together to resist the load acting on beam and thus the slab acts as a cover plate. Due to this we use a lighter steel section in composite construction
What are the Two Methods of Composite Construction in Buildings?
Method 1. In the first method, we cast the steel beam entirely in the concretion i.e steel beam encased in the concrete. The steel concrete bond is the main reason for composite action. The beam is laterally braced therefore the allowable stress in the flanges is 0.66Fy, where Fy is the yield strength, ksi (MPa), of the steel.
According to AISC, the cross sectional area of of bolts and threaded parts are designed for specified allowable unit tension and shear stresses. In case of seismic loads and wind loads in combination of gravity loads, we increase the allowable stresses by 1/3. Normally in case of direct tension, rivets are not recommended.
Bearing type connections are the most commonly used connection is building construction. In buildings, the allowable bearing stress Fp, ksi (MPa), on projected area of fasteners is
Fp=1.2 Fu
where
Fuis the tensile strength of the connected part in ksi (MPa).
