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From page 12... ... 12 C H A P T E R 3 Load Models and Calibration LRFD Limit-State Format The LRFD format is widely used for structural design of buildings, bridges, and other structures. In 1994, the AASHTO LRFD Bridge Design Specifications (LRFD-BDS) Read the entire page →
From page 13... ... 13 The Strength I limit state for dead load only (Comb. Read the entire page →
From page 14... ... 14 Category II: 7% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143, MRI = 700 Years) Read the entire page →
From page 15... ... 15 the few cases where it will be critical, it is close to the dead load combined with wind (Comb. Read the entire page →
From page 16... ... 16 The statistical parameters for m, f, and p were considered by various researchers, and the results were summarized by Ellingwood et al. Read the entire page →
From page 17... ... 17 The limit-state function can be written: , 1.0 1 1 2 2 3 3 4 4 2 ( ) = − +  − + g Q R Q R Q R Q R Q R i i The interaction equation is a nonlinear function; therefore, to calculate combined load-carrying capacity, Monte Carlo simulation was used for each random variable. Read the entire page →
From page 18... ... 18 To standardize the comparisons between ASD and LRFD, and for any specified-year wind, all analyses and comparisons are based on the total nominal moment for the LRFD 700-year total applied moment equal to 1.0: 1.07001M M MT D= + = and, the dead load moment can be represented by: 1 700M MD = − The calibration and comparisons vary the M700 wind load effect from 1.0 to 0.0, while MD varies from 0.0 to 1.0 so that the total applied nominal moment at the ASCE/SEI 7-10 700-year load remains 1.0. The total applied nominal moments for ASD and other LRFD year wind speeds is adjusted to be equivalent to the ASCE/SEI 7-10 700-year wind speed load case. Read the entire page →
From page 19... ... 19 and using that the nominal dead load moment and mean dead load moment are: 1 1 700 700 M M M M D D D ( ) = − = λ − where: lD = bias factor for dead load moment, The mean load effect on the structure becomes: 150 700 2 2 700Q M M M MD D P V X( ) Read the entire page →
From page 20... ... 20 The results for the Midwest and Western Region ASCE/ SEI 7-10 700-year wind speed are shown in Table 19 (other regions are similar) Read the entire page →
From page 21... ... 21 Using the ASCE/SEI 7-05 criteria for the ASD design, the wind moment for a 50-year wind speed is: 50 700 50 700 2 Design M M Design V V =   Considering that the Design V50 may differ from V50 = (lV) 2V700, a bias factor, lDesign, is introduced, and: 50 2 50 700 2 700 2 2 700 50 50 Design M V V M M Design V V Design Design V Design = λ   = λ λ λ = The total ASD design moment, MT3, consistent with MD + M700 = 1.0, becomes: 150 700 2 2 7003M M Design M M MT D Design V( ) Read the entire page →
From page 22... ... 22 and: , Cov , and are unchanged.lnQ Q Qσ The coefficient of variation for the strength (resistance) Read the entire page →
From page 23... ... 23 Notice that the total nominal moment, MT3, does not change, but the total design moment MD + M50I changes with the importance factor, resulting in different required nominal strength Rn. Similarly, for high importance, the required nominal strength Rn increases as shown in the following for the Midwest and Western Region. Read the entire page →
From page 24... ... 24 0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal Average Beta 700 Year LRFD ASD0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal Minimum Beta 700 Year LRFD ASD 0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal MinimumBeta 300 Year LRFD ASD 0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal Average Beta 300 Year LRFD ASD 0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal Average Beta 1700 Year LRFD ASD 0.00 1.00 2.00 3.00 4.00 00.511.5 Be ta MWind/MTotal MinimumBeta 1700 Year LRFD ASD Table 25. Minimum and average reliability indices (all regions) Read the entire page →
From page 25... ... 25 situation conducive to a traffic collision with the structure or a chain-reaction impact of vehicles. Ultimately, judgment is used to set the target reliability indices for the different applications. Read the entire page →
From page 26... ... 26 Other indices were computed for load ratios in each region. The results are illustrated in Appendix A Read the entire page →
From page 27... ... 27 Table 28. Sensitivity of the reliability index to load and resistance factors. Read the entire page →
From page 28... ... 28 The LRFD-LTS specifications were calibrated using the standard ASD-based specifications as a baseline. The variabilities of the loads and resistances were considered in a rigorous manner. Read the entire page →
From page 29... ... 29 (continued on next page) Example No. Read the entire page →
From page 30... ... 30 Example No. Title Graphic 12 Prestressed Concrete Light Pole 13 Luminaire Support – Fiber-Reinforced Polymer (FRP) Read the entire page →
From page 31... ... 31 Figure 5. Typical problem statement. Read the entire page →

From page 12...

... 12 C H A P T E R 3 Load Models and Calibration LRFD Limit-State Format The LRFD format is widely used for structural design of buildings, bridges, and other structures. In 1994, the AASHTO LRFD Bridge Design Specifications (LRFD-BDS)