scope:

1.0 OBJECTIVES AND SCOPE

This report documents the Phase I effort of the API Seismic Load Effects Study. It describes the methodology to be used to quantify the bias and uncertainty contained in the seismic load effects used in standard design practice.

The earthquake load effect, E, will be represented as the product of a nominal value, En, and random factors representing uncertainties in intensity, IE, and in analysis, AE:

E = En IE AE

The mean earthquake load effect, E, is given by:

E = En IE AE

where IE and AE are the means of I and A, respectively. The coefficient of variation (COV) of the load effect, VE, is given by:

V2E = V2IE + V2AE

where VIE and VAE are the COV's of I and A, respectively.

Phase II efforts focus on quantification of the earthquake load effects on platforms located at offshore California and Alaska sites. The references listed in Section 4 are used in this effort.

The foregoing results will be used by Professor Fred Moses to calculate the reliability indices, β, for current API working stress design, and to calibrate load factors, γE, and nominal load definitions suitable for seismic load and resistance factor design (LRFD).

The seismic design criteria will be:

where D and L are nominal dead and live load, γD and γL are their respective load factors, Rn is the nominal component resistance and φ is its resistance factor.

The remainder of the report is divided into four sections. Section 2 is an executive summary of the methodology, including an example problem. Section 3 is a detailed presentation of the methodology, including the identification and classification of all sources of bias and uncertainty. Section 4 is a list of references to be used for both Phase I--Methodology Development and Phase II--Quantification. Section 5 is a glossary of terms specific to either the seismic loading problem or the LRFD method.