5.Loads - Theory and Design of Structures I Structural...

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Unformatted text preview: Theory and Design of Structures I Structural Loads & Response Introduction All structures are composed of a number of interconnected elements. They enable the internal/external loads to be safely transmitted down to the ground, e.g. – slabs – beams – columns – walls – foundations Sequence of load transfer Reactions “Loads” R 1 R 2 R 1 R 2 It is usually assumed that the reaction from one element is a load on the next Sequence of load transfer From roof slab to beam From floor slab to beam From beam to column From beam to column From column to foundation Transfer of loading Sequence of load transfer – load path River Tributary Sequence of load transfer Sequence of load transfer is not clear. The design process The designer must make an assessment of the future likely level of loading to which the structure may be subjected during its design life. Determination of design loads acting on the structure Determination of design loads on individual elements Calculation of bending moments, shear forces and deflections of beams Sizing of beams Sizing of columns Nature of loading & design loads Nature of loading & design loads Seismic disturbance Live load Nature of loading & design loads Wind load (gusts) Temperature load (shrinkage?) Nature of loading & design loads Foundation settlement Impact Nature of loading & design loads It is usually assumed that the dynamic loads on the building structures can be reduced to equivalent static loads , e.g. – live loads – seismic disturbances – gusting of wind – movement of machinery Actual loading: dynamic (not static); changing For design: equivalent static load LL Æ uniform design load (on buildings) basic LL + impact allowance (on bridges) WL Æ equivalent static load (kN/m 2 of exposed surface area) EQL Æ equivalent static load (% of gravity load) Others: essentially STATIC Nature of loading & design loads Nature of loading & design loads The loads acting on a structure are divided into different basic types: – dead load – live load – wind load – earthquake load – loading from other sources For each type, the characteristic and design values must be estimated The designer will have to determine the particular combination of loading which is likely to produce the most adverse effect on the structure in terms of bending moments, shear forces, deflections, etc. Nature of loading & design loads Live load Wind load Max axial load Combination of loading Most adverse effects Dead Loads (DL) Dead Loads (DL) DLs are all the permanent loads acting on the structure including: – self-weight – finishes – fixtures – partitions Dead Loads (DL) Estimation of the self-weight of an element – cyclic process since its value can only be assessed once the element has been designed LL DL ? ? Dead Loads (DL) Assume a cross-section DL BM, SF, etc Check if OK Revise cross- section Yes No End LL Economical?...
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This note was uploaded on 12/01/2010 for the course CIVL 2007 taught by Professor Profchai during the Spring '10 term at HKU.

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5.Loads - Theory and Design of Structures I Structural...

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