Deflection Limits of Steel and Timber Beams Based on Safety Targets
In the reliability assessment and health monitoring of existing structures,beam deflection is not only a direct reflection of the normal service performance of structural members,but also a reflection of the safety status of structural members.Aiming at the safety control of structural members,this paper proved that the deflection to span ratio of beams is directly proportional to the maximum tensile strain and the comprehensive coefficient of deflection to span ratio.The comprehensive coefficient of the deflection-span ratio was validated using data from experimental references on the flexural performance of steel and timber beams.The synergistic effect of concrete floor slabs and steel beams affects the deflection to span ratio by increasing the height of the section,changing the height of the section neutral axis,sliding between the concrete wing slab and the steel beam,and changing the stiffness in negative moment area.The comprehensive influence coefficient is about 0.64～0.83.The synergistic effect of timber floors and timber beams has little effect on the deflection to span ratio,but wood creep causes a significant increase in the long-term deflection of timber beams.A beam deflection graded control method based on the maximum tensile strain limit was established.Compared with the deflection limit value in current standards,the results show that the deflection limits proposed in this paper has a clear safety control target,and is significantly different according to the change of the specific force characteristics of the beams.The range of the deflection limit is wider,more adaptable and more accurate than the current standard,and can be used as a reference for reliability identification and structural health monitoring of existing structures.
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