Download - Buiilding Loads
BUILDING LOADS
Design
Strength
Loads
ReinforcementRatio
Member Dimension
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.
Building Codes
Buildings must be designed andconstructed according to the provisions of abuilding code, which is a legal documentscontaining as requirements related to suchthings as structural safety, fire safety, plumbing,ventilation, and accessibility to the physicallydisabled.
A building code has the force of law and isadministered by a government entity such as acity, a county, or, for some large metropolitanareas, a consolidated government.
Building codes do not give designprocedures, but they do specify the designrequirements and constraints that must besatisfied.
i.e. For structural engineer the prescription of minimum live loads for buildings.
Three National Code Organizations
• Uniform Building Code (west of Mississippi)
• Standard Building Code (southeastern states)
• BOCA National Building Code (northeastern country)
where BOCA stands for Building Officials and Code Administrators)
Unified building code- International Building Code
Design SpecificationsGives more specific guidance for the design ofstructural members and their connections.They are periodically revised and updated by theissuance of supplements or completely neweditions.
For steel;
1. American Institute of Steel Construction (AISC)- design of steel buildings and their connections.
2. American association of State Highway and Transportation officials (AASHTO) – covers the design of highway and bridges related structures. It provides for all structural materials normally used in bridges, including steel, reinforced concrete, and timber.
3. American Railway Engineering and Maintenance-of-Way Association (AREMA)-covers the design of railway bridges and related structures.
4. American Iron and Steel Institute (AISI)- deals with cold-formed steel.
8
Types of Loads
• Determination of loads for which a given structure may be designed for is a difficult problem.
Questions to be Answered:
• What loads may structure be called upon during its lifetime?
• In what combinations these loads occur?
• The probability that a specific live load be exceeded at some time during lifetime of structure?
SCOPE OF THE LECTURE
• Types of loads.
• Static and dynamic 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
50 psf
100 psf
Dynamic loads
The other group of loads is the dynamic loads , and the following are types of such loads:
Wind load Blast load
Impact load Flood loadSeismic load
13
1. Dead load
Dead Loads consist of the weight of all materials and fixed equipment incorporated into the building or other structure.
– Weight of structure
– Weight of permanent machinery etc.
– Dead loads can be reasonably estimated if the member dimensions and material densities are known.
Types of Loads
14
2. Live load:
Live loads are those loads produced by the use and occupancy of the building or other structure and do not include dead load, construction load, or environmental loads.
– Weight of people, furniture, machinery, goods in building.
– Weight of traffic on bridge
Types of Loads
CE-409: Lecture 03 Prof. Dr. Akhtar Naeem Khan15
Live loads for various occupancies
Occupancy Live load,psf
Residential 40
Libraries(reading room) 60
Mercantile 75-125
Heavy manufacturing 125-150
Light storage 120-125
Heavy storage 250 minimum
Types of Loads..
2. Live load: (UBC Table 16-A)
Load Example: Live Load in Ballroom
Live Load = 100 lb/ft^2Ballroom
17
The 40psf L.L specified by code for Residential Buildings is too
Conservative to account for the uncertainties in structural actions
Such as impact, fatigue, temp. effects etc.
Types of Loads2. Live load:
Types of loads
3. Environmental Loads
Environmental loads include wind load, snow load, rain load, earthquake load, and flood load.
18
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.
Earthquake Loads
• Structure loaded when base is shaken
• Response of structure is dependent on the frequency of motion
• When frequencies match with natural frequency of structure - resonance
Load Example: Earthquake Load
Base Motion
Earthquake Load
Earthquake Load
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.