长沙理工大学：《结构设计原理》课程教学资源（PPT课件）Chapter 2 Probablisitic Limit States Design Method

JPKIC 结构计原黑 Chapter 2 Principle of Structure Design and Calculation Based on Probabilostic Limit State Method

Chapter 2 Principle of Structure Design and Calculation Based on Probabilostic Limit State Method

JPKIC Main content 箱构设计原黑 History and basic concept of methods for calculation and design Functional requirement of structure Conception of limit state,probabilistic limit state design method Design method,principles,expressions and factors of existing Codes Strength of Materials,action classifications,action combination

Main content ⚫ History and basic concept of methods for calculation and design ⚫ Functional requirement of structure ⚫ Conception of limit state, probabilistic limit state design method ⚫ Design method, principles, expressions and factors of existing Codes ⚫ Strength of Materials, action classifications, action combination

JPKIC 结构设计原理 §2.0 Introduction hepniiplestncturedesgn 1,The Purpose of Structural Design Design structures meeting functional requirements, comparing the action effects from outside environment and its resistance to reach the objectives of safety and economy Specifically,Design is to determine cross-sectional size, area of reinforcing bar and construction requirements

§2.0 Introduction 1、The Purpose of Structural Design Design structures meeting functional requirements, comparing the action effects from outside environment and its resistance to reach the objectives of safety and economy Specifically, Design is to determine cross-sectional size, area of reinforcing bar and construction requirements

JPKIC 2.History of structural design 结构热试原得】 From Gelieo age to present,300 years,the design can be summarized from two aspects: 1)structural design theory, theory of elasticity limit state theory 2)Structural design method deterministic design method probabilistic design method

2、History of structural design From Gelieo age to present, 300 years, the design can be summarized from two aspects: 1) structural design theory, theory of elasticity limit state theory 2) Structural design method deterministic design method probabilistic design method

JIPKIC 结构线其原黑 3,Theory and method of structural design and calculation Allowable stress method ](1860 year) ●Fracture design method」（l932year) Multi-factor limit state design method(1970 year) Probabilistic limit state design method based on reliability theory,this is a objective for engineers

3、Theory and method of structural design and calculation ⚫ Allowable stress method ](1860 year) ⚫ Fracture design method ]（1932year） ⚫ Multi-factor limit state design method(1970 year) ⚫ Probabilistic limit state design method based on reliability theory, this is a objective for engineers

2.0.1 Allowable stress method JIPKIC 结构盘计原课 l、Basic concepts Allowable [stress method ]-a maximum stress of a section reach or exceed allowable stress,and then element fails o s[o]= strengthof material safety factor o.≤o.]=A concrete stress RC member Steel stress Where :k and k are stafey factors

   safety factor strength o f material    =   c c c c k f    =   s s s s k f    = RC member： concrete stress Steel stress Where ： are stafey factors. s k and k c 1、Basic concepts §2.0.1 Allowable stress method Allowable [stress method ]—a maximum stress of a section reach or exceed allowable stress, and then element fails

JPKIC RC structures as an example 结构设计原理 jhepniheipledstucturedesgn Assume steel and concrete as elastic material Plane section assumption that deformation keep a section The tensile strength of concrete may be neglected ● Strains of steel and concrete at contact are equal &=8 E bx h A b Schematic of allowable stress method of RC element

c  RC structures as an example ⚫ Assume steel and concrete as elastic material ⚫ Plane section assumption that deformation keep a section ⚫ The tensile strength of concrete may be neglected ⚫ Strains of steel and concrete at contact are equal b x h s  s As    c c bx  2 As Schematic of allowable stress method of RC element s ci  = 

JPKIC 2、features 结构设计原黑 1,safety factor K>1,a lager k will have a higher safety and more material. 2.Without consideration of diversity of function 1 )load-carrying capacity. 2)service performance,crack and deformation. 3,The determination of safety is by experience judgment and no scientific basis. 3,applicable condition Non-line-shape structures,such dam,spatial shell structures. No equations in code.So elastic mechanism method is a useful tool

2、features 1、safety factor K >1, a lager k will have a higher safety and more material. 2、Without consideration of diversity of function 1）load-carrying capacity. 2) service performance, crack and deformation . 3、The determination of safety is by experience judgment and no scientific basis. 3、applicable condition Non-line-shape structures, such dam, spatial shell structures. No equations in code. So elastic mechanism method is a useful tool

JPKIC 结构计原黑 S 2.0.2 Fracture design method -1930s l、basic concept The inner force reaches ultimate inner force under loading, and then element fails.Taking flexural RC element as an example,as M≤M./k where is the inner force of section,is ultimate inner force of a cross section,k is a safety factor

§2.0.2 Fracture design method ——1930s 1、basic concept Mu M M k  u M The inner force reaches ultimate inner force under loading, and then element fails. Taking flexural RC element as an example, as where is the inner force of section, is ultimate inner force of a cross section, k is a safety factor

JIPKIC 结构设计原理 RC structure as an example The principle of structure design Fracture stage as a basis Without consideration of concrete tensile strength Equavilent rectangular stress block for computation bx h A Schematic of fracture stage of RC element

b x h As 0 h s As f   c c f bx  2 Schematic of fracture stage of RC element RC structure as an example ⚫ Fracture stage as a basis ⚫Without consideration of concrete tensile strength ⚫Equavilent rectangular stress block for computation