Technological University (Sagaing)
Department of Civil Engineering
Chapter 3
Loads
Presented By
Group - I
( Fourth Year )
1
Content
➢ Introduction of Loads
➢ Types of Loads and Its Briefs
➢ Conclusion
2
Introduction
➢ Structural framing should be designed as stipulated by the governing
building code, to sustain the various loads.
➢ The design loads and the method of applying them are based on the
from the authoritative sources such as nationally recognized standards,
accepted engineering practices, published material of engineering and
research agencies and societies.
3
Types of Loads
The various types of loads for design purposes are
Dead Loads
Live Loads
Snow Loads
Wind Loads
Impact Loads
Earthquake Loads
4
Dead Loads
➢ Dead loads are constant in magnitude and fixed in location
throughout the lifetime of the structure.
➢ They are gravity loads that consist of the weight of the structural
members and all material fastened there to or permanently supported
there by.
5
Live Loads
➢ Live load may be defined as the weight superimposed by the use or
occupancy of a building or other structures, but excluding wind, snow,
earthquake, or dead load.
➢ Live loads are gravity load.
6
Floor Live Loads
➢ Floor should be designed to safely support the dead load, the
uniformly distributed load or the concentrated load, whichever
produce the greater stress.
➢ For floor live loads of 100 psf or less, the design floor live load should
be reduced to N or 60%.
➢ For floor live loads exceeding 100 psf, no reduction should be made,
except the design floor live loads on columns may be reduced 20%.
7
Reduction Factor Formula
D. L
N = 23.1 + 1 +
L. L
Where:
N = Reduction factor (%)
D.L = Dead load/ sq.ft of supported member
L.L = Design floor live load/ sq.ft of supported member
8
Roof Live Loads
➢ Roof live loads should follow the governing building code.
➢ In the absence of a governing code, the minimum roof live loads for
flat, pitched, or curved roofs are given in Table 3.4.
➢ Roofs must resist either the minimum loads or the snow load,
whichever causes the greater stress.
9
Snow Loads
Factors affecting snow load accumulation on roofs include
Elevation
Latitude
Wind frequency
Duration of snowfall
Roof geometry
Site exposure
Snowfall varies from year to year and the design should be based on
the maximum recorded snow load.
10
Ground Snow Loads
➢ Ground snow loads determine the roof loads in mountain regions.
➢ Use the following formula to calculate ground snow loads in the
mountain regions.
2
L
SL = 2.3 + EL + − 8.5
4
Where:
SL = Ground snow load
EL = Elevation (ft)
L = Latitude (degree)
11
Roof Snow Loads
➢ The roof snow load is a function of the geometry of the roof and the
exposure to wind forces.
➢ For the design of both ordinary and multiple series roofs, either flat,
pitched or curved a basis snow load coefficient of 0.8 should be used
to convert ground snow load to a roof snow load.
➢ For roofs exposed to winds of sufficient intensity to blow snow off,
the basic snow load coefficient can be reduced to 0.6.
12
Wind Loads
➢ Designing structure to resist wind loading is a very complex
engineering problem.
➢ With the high velocity winds, low pressure areas are created on the
building which creates suction pressure.
➢ Wind load data from Uniform Building Code,1997 (UBC 97) are
used as follow:
• Exposure type • Important factor (I)
• Exposure height • Windward coefficient (Cq)
• Basic wind speed • Leeward coefficient (Cq)
13
Basic Wind Loads
➢ Wind probability maps for 50 and 100-year mean recurrence intervals
are plotted for design purposes.
➢ These figures provide basic wind velocities for observed air-flows at a
height of 30 ft above the ground.
➢ Since the wind velocities given mostly for a height of 30 ft, it is
necessary to modify this value for other design height.
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Equation of Wind Velocity
1/𝑥
h
Vh = V30
30
Where:
Vh = Wind velocity at any height
V30 = Wind velocity at a height of 30ft
h = Height of building
x = Exponent depending upon site exposure conditions
For level terrain, x=7
For sub-urban area, x = 5
For urban areas, x=3 15
Earthquake Loads
➢ Potentially damaging ground movements produced by sudden release
of energy along faults in the earth’s crust is called earthquake.
➢ Earthquake loads consists of the inertial forces of building mass that
result from the shaking of its foundation by a seismic disturbance.
➢ The lateral force provisions are based on the 1970 edition of the
Uniform Building Code (UBC) to ensure minimum design standards
for earthquake-resistant structures.
➢ Every building should be designed and conducted to withstand
minimum total lateral seismic forces.
➢ These forces are assumed to act non-concurrently in the direction of
each of the main axes of the building. 16
Equation for Total Lateral Load (V)
V = ZKCW
Where:
V = Total lateral load or shear at base (lb)
Z = Numerical coefficient depend on the zone
K = Numerical coefficient
C = Numerical coefficient for base shear
W = Total dead load (lb)
17
Factors to consider for base shear imposed by earthquake
• Soil profile type • Seismic force amplification factor
• Seismic source type • Response modification factor
• Seismic zone factor • Seismic response coefficients
• Seismic important factor • Seismic base shear coefficient
• Near source factor • Distance from seismic source
Moving Loads
➢ When the maximum vertical shear due to a single moving
concentrated load is being calculate, the load is placed at a distance
from one support equal to the depth.
➢ For simple beams, the maximum bending moment produced by
moving loads occurs when that load is as far from one support as the
center of gravity of all moving loads.
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Conclusion
➢ In conclusion, structural framing must be carefully designed to meet
the requirements set by the governing building codes to ensure safety
and stability.
➢ The design loads, including dead loads, live loads, snow loads, wind
loads, impact loads, and earthquake loads, must be considered and
applied following authoritative sources and recognized engineering
standards.
➢ Following these guidelines ensures structures can withstand various
forces and remain safe and durable.
20
Thank you
for your attention!
