Transcript LOADS ON BUILDINGS

LOADS ON BUILDINGS
Lecturer : Dr. Ali Naji Attiyah
DESIGN PROCESS
Design is the determination of the
general shape and all specific
dimensions of a particular structure
so that it will perform the function
for which it was created.
So , good design must be safe and
economic.
Member
Dimension
Loads
Design
Process
Strength
Reinforcement
Ratio
SCOPE OF THE LECTURE
• Types of loads.
• Static and dynamic loads.
• Dead and live loads.
• Blast loads.
• Seismic loads.
TYPES OF LOADS
Loads are classified as static and dynamic . Static loads are independent from
time but dynamic loads are function of time.
Dead and live
loads are types of
static loads.
Dead loads are
those have
unchangeable
locations in
structure and their
values are certain
and constant .
Live loads are those
movable and their
values are uncertain.
Dead loads are calculated easily using structure dimensions and material density .
Live loads are movable and their values are uncertain , so they can not be
calculated directly and local or international specifications shall be consulted.
International Building Code IBC 2009 published live load values dependent on
types of building occupancy.
80 psf
100 psf
50 psf
Dynamic loads
The other group of loads is the dynamic loads , and the following are types of such loads:
Blast load
Wind load
Impact load
Seismic load
Flood load
BLAST LOADS
Blast loads are an increase in atmosphere pressure which make buildings applied to
uniform pressure . Blast pressures increases with increasing TNT weight and vice versa
if the explosion distance is increased.
Example1
If a building is designed to
carry 0.5 psi overpressure
safely, evaluate the required
stand-off distance for small
cars.
Example2
Can the same building
withstand an explosion
of a truck carrying
10000 pounds of TNT
at a distance 1500
foots ?
SEISMIC LOADS
Seismic loads on buildings are caused by movement in foundations . The acceleration of this
movement is very rapid and its value
is highly increased with height.
Different types of failure are found in the same earthquake , because of different modes
of movement.
Seismic load is applied as horizontal shear at the building base. The shear force is
proportional to the building weight (W) and calculated from :
V = Cs . W
Cs is the seismic response coefficient which is found from :
Cs = SDS / ( R/I)
R is the response modification factor , which is dependent on the type of structure and
can be found from the table below.
I is the importance factor ,which is dependent on the occupancy category and is taken
1.25 for building designed for more than 300 person and 1.0 for ordinary building.
SDS is the design acceleration response , which is function of the earthquake ground motion.
Countries all over the world have seismic maps and the designer can evaluate SDS directly.
Unfortunately, for our country there is no such map , so, the value of SDS should be
estimated for Iraq.
Estimate a similar
seismic zone between
Iraq and USA…
Choose the proper contour for Najaf and note that the numbers are measured as percentage
from the ground acceleration (%g).
Compare the value of the design acceleration response SDS for Najaf with that prepared by
others.
Example
For a reinforced
concrete ordinary
building , find the
horizontal seismic
shear shall be
applied at the base
level. Note that the
building will be
constructed at Najaf.
Ans: 0.062 W
QUESTIONS ?