China
Africa
Explore chapters and articles related to this topic
Philosophy of design
Published in Chanakya Arya, Design of Structural Elements, 2022
This chapter has examined the bases of three philosophies of structural design: Permissible stress, load factor and limit state. The chapter has concentrated on limit state design since it forms the basis of the design methods given in the Eurocodes. The aim of limit state design is to ensure that a structure will not become unfit for its intended use, that is, it will not reach a limit state during its design life. Two categories of limit states are examined in design: Ultimate and serviceability. The former is concerned with overall stability and determining the collapse load of the structure; the latter examines its behaviour under working loads. Structural design principally involves ensuring that stresses due to the loads acting on the structure do not exceed its strength and the first step in the design process then is to estimate the loads acting on the structure.
Limit state design in geotechnics
Published in K.S. Li, S-C.R. Lo, Probabilistic Methods in Geotechnical Engineering, 2020
K. S. Li, I.K. Lee, S.-C. R. Lo
The major advantage of the limit state design method is that it provides a formal framework whereby the uncertainties involved in a geotechnical design and the bias of the design method used for analysis can be taken into account. The design procedures based on the limit state design approach may be slightly more complicated that the conventional FOS approach. However, there are real benefits to be gained from using the limit state design method. If the designer is willing to spend more effort in reducing the uncertainties involved in the design, such as by means of implementing a more extensive laboratory and field testing programmes or full scale loading tests, he will be able to use a higher partial factor for the design resistance, and hence a less conservative design can be achieved. In the conventional FOS approach, it is difficult to judge to what extent the minimum factor of safety can be reduced when the uncertainties involved in the design have been maximised through a more elaborate site investigation programme.
Stochastic finite element model error for unreinforced masonry walls subjected to one way vertical bending under out-of-plane loading
Published in Jan Kubica, Arkadiusz Kwiecień, Łukasz Bednarz, Brick and Block Masonry - From Historical to Sustainable Masonry, 2020
A.C. Isfeld, M.G. Stewart, M.J. Masia
The degree of spatial variability in material properties is known to be higher in masonry than in other common structural materials. This variation increases the complexity when determining the overall strength of a structural element. In limit states design safety factors are used along with deterministic analysis techniques to account for uncertainty and assess the reliability of a structure. The Australian Standard for Masonry Structures (AS 3700, (2018)) follows a limit states approach, using the lower five-percentile values of characteristic strengths with capacity reduction factors. The direct outcome of random and spatial variability cannot be directly quantified with this approach. When a wall is subjected to vertical flexure the bending moment varies over the height of the wall. As bond strength varies along both the wall height and length, failure will initiate where the ratio of applied bending moment to moment resistance first becomes critical. The importance of quantifying the variability in joint strength, and subsequent variability in wall panel strength has been established by Baker and Franken (1976), Baker (1981), and Lawrence (1983). Lawrence and Stewart (2002) developed a structural reliability model accounting for unit-to-unit variability in bond strength. Heffler et al. (2008), examined the unit-to-unit spatial correlation of flexural tensile bond strength within masonry walls. Analysis of bond wrench testing data gave an average correlation coefficient of ρ = 0.4 within courses of masonry, with each unit’s flexural bond strength being represented by a truncated Normal distribution.
A re-evaluation of the hull girder shakedown limit states
Published in Ships and Offshore Structures, 2019
A ship hull girder undergoes significant longitudinal bending due to the imbalanced distribution of its weight and the buoyancy (still-water bending moment) as well as the external wave actions (wave-induced bending moment). Therefore, the longitudinal strength of a ship hull girder becomes one of the most fundamental aspects of the ship structural integrity (Yao and Fujikubo 2016). Two philosophies are commonly employed in the design of ship structures, namely the allowable stress principle and the limit state design. In the former, the determination of structural scantlings are based on the criterion that maximum resultant stress under a prescribed loading does not exceed the allowable stress specified by relevant stakeholders. Although the allowable stress principle provides practical design guidelines, it is not able to determine the true safety margin against extreme conditions for ship structures. To this regard, a limit state design philosophy can be employed where all of the possible failure modes are explicitly taken into account in the estimation of structural capacity (Paik and Thayamballi 2003). Four limit states are commonly identified for ship structures, namely serviceability limit state, ultimate limit state, fatigue limit state and accidental limit state.
Performance-based analysis and design for internal stability of MSE walls
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2019
Richard J. Bathurst, Tony M. Allen, Yoshihisa Miyata, Sina Javankhoshdel, Nezam Bozorgzadeh
A shortcoming of the approach described above to compute COVRn and COVQn is that it does not account for other sources of uncertainty beyond simply the variability in soil and reinforcement properties. In LRFD foundation engineering practice in Canada, the notion of level of understanding has been introduced to account for uncertainty in the calculation of nominal values at time of design. The motivation is to reward geotechnical design engineers with larger resistance factors in limit state design equations as knowledge of project ground conditions and material properties improve (Fenton et al. 2016; CSA 2019). Bathurst, Javankhoshdel, and Allen (2017) assigned values of COVRn and COVQn equal to 0.10, 0.20 and 0.30 corresponding to high, typical and low levels of understanding, respectively. These assignments were necessary to quantify levels of understanding for reliability theory-based LRFD calibration but are equally applicable for reliability-based analysis and design described in this paper. The exception to these values is the assignment of COVRn = 0 for the nominal strength of the geogrid or steel reinforcement that appears in the tensile limit state function for these structures. This is because there is no uncertainty in the calculation of the nominal tensile strength at time of design which is taken as deterministic; rather, all uncertainty is captured by the bias statistics for the tensile strength model.
Philosophies of bamboo structural design and key parameters for developing the philosophies
Published in Cogent Engineering, 2022
Leule M. Hailemariam, Ermias A. Amede, Ezra K. Hailemariam, Denamo A. Nuramo
Limit state design can be thought of as a middle ground between allowable and load factor methodologies. It is a more comprehensive strategy that adequately considers both methodologies. Most modern building regulations are based on the limit state approach. The limit state philosophy forms the basis of the design methods in most modern regulations.