46078818 combartinations of loads

7/30/2019 46078818 Combartinations of Loads

1/9

COMBINATIONS OF LOADS


2/9


Buildings, towers & other structures and allportions thereof shall be designed to resist theload combinations specified in section 203.3 or

203.4 & where req. By section 208 & the specialseismic load combinations of section 203.5

The most critical effect can occur when one ormore of the contributing loads are not acting. Allapplicable loads shall be considered, includingboth earthquake & wind, in accordance w/ thespecified load combinations.


3/9

SYMBOLS AND NOTATIONS

D - Dead load

E Earthquake load

Em estimate max earthquake

F Load due to fluids w/ well defined pressures & max heightsH Load due to lateral pressure of soil & water in soil

L Live load

Lr Roof live load

P Ponding loading

R Rain load on the undeflected roofW load due to wind pressure

T self straining force & effects arrising from construction orexpansion resulting from temp. Change, shrinkage, moisturestorage, creep in component materials movement due todifferential statement on combinations therof.


4/9


This code requires the use of allowable stressdesign of wood members and their fastening(see NSCP 2001 section 601 & 604). NSCP

section 203.4 permits two differentcombinations of load method. These are:

1. Allowable stress design (ASD) of NSCP 2001

section 203.4.12. Alternate allowable stress design of NSCP 2001

section 203.4.2


5/9

ALLOWABLE STRESS DESIGN

Is a method of proportioning & designing

structural members such that elastically

computed stresses produced in the membersby nominal loads do not exceed specified

allowable stress.


6/9

ExampleThis method is done for plywood shear wall shown below. The wall ina light wood framed building.


7/9

The information is given:

Zone 4 Ca = 0.40 I = 1.0 p = 1.0

VE = 17.84 (seismic force determined from NSCP 2001 section 208.5.2)

Gravity Loads:

Dead WD = 0.30 KN/linear meter (tributary load, including weight ofwall)

LIVE WL = 0.00 (Roof load supported by other elements).

Determine the required design for shear capacity q and hold-downcapacity T for the following load combinations:

1. Basic allowable stress design

2. Alternate allowable stress design


8/9

1.BASIC ALLOWABLE STRESS

DESIGN The governing load combinations for basic allowable stress design are NSCP

2001 equations (203-9), (203-10), (203-11). These are used w/o the usual 1/3 stressinc. Except as permitted by NSCP 2001 section 308.2 for soil pressure. For wooddesign, however, the allowable stresses for short-time load due to wind orearthquake may be used.

D + E / 1.4 NSCP equations (203-9)

0.9 D E / 1.4 NSCP equations (203-10)

D + 0.75L + 0.75E / 1.4 NSCP equations (203-11)

Where:

E = pEh + Ev = 1.0 Eh + 0 = Eh NSCP equations (208-1)

Note that under the provisions of NSCP 2001 section 208.5.1.1. Ev is taken as zero inASD.


9/9

ALTERNATE ALLOWABLE STRESS

DESIGN Under this method of load combination, the customary 1/3

inc. In allowable stress is allowed. The governing loadcombinations, in the absence of snow load are the ff:

D + L + E/1.4 NSCP equations (203-14)

0.9D E /1.4 NSCP equations (203-10)

Where:

E = pEh + Ev = 1.0 Eh + 0 = Eh NSCP equations (208-1)

Note that under the provisions of NSCP 2001 section208.5.1.1. Ev is taken as zero in ASD.

46078818 combartinations of loads

Documents