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doc uploaded be Aeysha states that,'Note that the horizontal component of Em is Ω0 times the seismic force E (not Ω0 E/1.4); thus if allowable stress design is being utilized and the analysis results are in terms of a reduced element seismic force E/1.4,that force must be multiplied by 1.4 to be used in this equation in order to be compared to member strength'. read part in blue,and tell me what u make of it. Em is defined as maximum earthquake that can be transferred by continuous member to supporting member and max earthquake force should be Em not Em/1.4.Em/1.4 will be sort of service level force.

There are 2 things.. First, the 1/3 rd stress increase for soil pressures shouldn't be taken for granted, and shall only be be used after due consultation with the geotechnical engineer. I dont have a code reference for 33% thing but if It isn't mentioned in the code, it is commonly allowed by the Geotech engineer. The following note is from the geotech report for a current project. "The net allowable bearing pressure may be increased by one-third for transient wind or seismic loads." Second, Another possible alternative would be to reduce forces and have a economical design , The 25% reduction applied to the overall overturning moment at the base of the structure due to lateral seismic forces (talking about the big picture here - not moment on an individual footing). As the structure overturning moment is generally resolved into a force couple in braced frames or individual moments in footings, I read this as allowing a reduction in either the force couple or the individual moments for design, both strength and stability, of the footings. As basis see the 2009 NEHRP Provisions which basically provide a commentary to ASCE 7-2005 (downloadable - big file - here: http://www.fema.gov/...cord.do?id=4103) which says for this provision (emphasis added): C12.13.4 Reduction of Foundation Overturning. Since the vertical distribution of forces prescribed for use with the equivalent lateral force procedure is intended to envelope story shears, overturning moments are exaggerated. (See Section C12.13.3.) Such moments will be lower where multiple modes respond, so a 25 percent reduction is permitted for design (strength and stability) of the foundation using this procedure. Note:This 25% reduction is for seismic only.

1.2 D + f1L + 1 Em 0.9D +/- 1 Em

@Hasan, The document I posted says explicitly that product of Omega*Horizontal Force should be used: same as what baz is saying.

thanks alot for your response.........let me study it first

Good Job! On a lighter note, Life is full of surprises. Specially if you are a structural engineer.

i was making load combinations for descon new project. it was strange when i found out they are unaware of vertical component of earthquake. Except one project they don't take this. further more they are also unaware of special seismic combinations. but one thing is encouraging tht they most deal with steel structures and when we use ASD Ev is zero. This clause has saved them till yet

You're welcome Hasan cheers!

thanks sir for such explainatory answer.

No clue about ASD. Your last resort would be UBC 97 Commentary.