An-Najah University Journal for Research - A (Natural Sciences)

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Keywords

• Stochastic Finite Element
• Reliability Analysis
• Live Load Reduction Factor
• Design Codes

Abstract

According to most building codes, the axial live load effect in columns of multi-story buildings may be reduced by some reduction factor. The justification for such a reduction is that there is a small probability for having all spans and floors of the building occupied with a nominal live load value. While this justification is jointly adopted by all buildings codes and standards, there are significant variations in the degree of reduction as allowed by these building codes. A probable cause for such significant variations is that these reduction factors were not based on reliability analyses, but rather on some extrapolation of different stochastic live load models to multi-story buildings. This study re-establishes the live load reduction factors based on reliability analysis, specifically, by maintaining the same reliability index for the columns. To achieve this goal, Monte-Carlo technique is utilized through the finite element software “ANSYS” on several thousand models of multi-story buildings. Live load, geometric and material variabilities are taken into consideration at many levels of statistical representation. The resulting stochastic F.E. analysis gives the probabilistic distribution of axial live load in columns, which is then used to re-calculate the characteristic “nominal” value for the axial live load based on a reliability index. The obtained “nominal” value of axial live load in columns is then compared to the axial live load value obtained using nominal load value as given in codes and standards distributed uniformly over all spans and floors of the building. Based on this comparison, the reduction factor is readily defined as the ratio between the two values. The resulting reduction factors are then compared to those given in codes and standards and conclusions are then drawn.

معلومات المقال

قيد النشر

الكلمات الإفتتاحية

• Stochastic Finite Element
• Reliability Analysis
• Live Load Reduction Factor
• Design Codes

الملخص

According to most building codes, the axial live load effect in columns of multi-story buildings may be reduced by some reduction factor. The justification for such a reduction is that there is a small probability for having all spans and floors of the building occupied with a nominal live load value. While this justification is jointly adopted by all buildings codes and standards, there are significant variations in the degree of reduction as allowed by these building codes. A probable cause for such significant variations is that these reduction factors were not based on reliability analyses, but rather on some extrapolation of different stochastic live load models to multi-story buildings. This study re-establishes the live load reduction factors based on reliability analysis, specifically, by maintaining the same reliability index for the columns. To achieve this goal, Monte-Carlo technique is utilized through the finite element software “ANSYS” on several thousand models of multi-story buildings. Live load, geometric and material variabilities are taken into consideration at many levels of statistical representation. The resulting stochastic F.E. analysis gives the probabilistic distribution of axial live load in columns, which is then used to re-calculate the characteristic “nominal” value for the axial live load based on a reliability index. The obtained “nominal” value of axial live load in columns is then compared to the axial live load value obtained using nominal load value as given in codes and standards distributed uniformly over all spans and floors of the building. Based on this comparison, the reduction factor is readily defined as the ratio between the two values. The resulting reduction factors are then compared to those given in codes and standards and conclusions are then drawn.