Assignment on Girders Bridge
Added on 2020-05-04
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Bridge AssignmentStudent’s NameInstitutionCity Country
Girders 2IntroductionNeighbouring structures can get damaged due to pounding if they are too close to one another. Even with the added research done and the extra recommendations recently included, the pounding damage in the bridge girders is still a major observation when earthquakes occur. The recent regulations have a recommendation that these adjacent structures need to be properly separated to avoid colliding the recommendation is made from the assumption of experience of similar ground excitation[ CITATION Lee13 \l 1033 ]. Also, their behaviors are produced form the study of structural properties. If one takes the case occurring in nearby buildings, the taken assumption regarding similar ground excitation can be justified. Caution needs to be taken on the various footing properties together with the non-uniform conditions on the ground. Interactions between the concerned subsoil and buildings. In the cases of many constructed bridges, the use pier supports is another reason that can lead to the production of theout-of-phase response of the adjacent spans of bridges. In cases that relate to the later, using current recommendations of designs can lead to an adverse effect[ CITATION Sve13 \l 1033 ]. The use of minimum spacing between structures is a major measure that allows avoidance of pounding damage. When bridges are concerned, using large spacing between neighboring girders will heavily affect the usage of traffic across them. The adjusting of fundamental frequencies in adjacent bridge structures could fail to be a good method that is sufficient or better suited to the approach to reducing out-of-phase responses. This is due to the feature of bridge structures to have the tendency of experiencing non-uniform spatial ground excitation[ CITATION Par01 \l 1033 ]. This proposal aims at designing a new philosophy on the bridge girders. Bridge girder movements.Various sources induce movement relative to girders, they are; ground motion spatial vibration, uneven vibration properties in nearby structures of bridges and the variation of the interaction of soil structures
Girders 3due to the shifting properties of soil at the supports of bridges due to the variety of slenderness ratio and footings in neighboring bridge piers[CITATION Imp \l 1033 ]. The forces of inertia are activated by the excitation vibration in the constructed structure. If say the structure put up is low, the footing of such a construction is most probably to move laterally from one side to another. Movements like these initiate pressure waves at either footing sides together with the development of shear waves coming from the lowers interface of the structure footing. When such movements are experienced by tall structures, the concerned structure rocks at its footing due to the movement that leads to the whole structure bending[ CITATION Jin10 \l 1033 ]. Movements in the footing mainly activate the pressure waves in either foot edges together with the development of shear waves in the same footings. Taking note that when a footing vibrates waves are produced, various footing movement lead to various wave propagation and also a variety of soil stiffness dynamics and damping in radiation will be developed[ CITATION Sei07 \l 1033 ]. Long-extended structures such as bridges are majorly influenced by the role of soil. Recalling that seismic waves require some duration to move from a footing bridge pier to the next support pier, exaction of grounds at the nearby support experience some delay. Also, the properties of soil in support of bridges are non-uniform and heterogeneous. This, therefore, means that the motions in the ground inthe concerned support is incoherent[ CITATION Tee13 \l 1033 ]. Also, the structural response to the varying spatial ground excitation is not similar to the common ground motions that are uniform. Bridge structures have spatial variations that lead to a variety of relative response between the nearby bridges segments like the ones put under the assumption of bridge segments experiencing similar ground motion[ CITATION MJP96 \l 1033 ]. Taking note that any nearby bridge segment varies in slenderness, though they are from similar fundamentally fixed frequency base and are influenced by similar ground excitation with bridge pier
Girders 4subsoil being uniform in their properties, the response between the bridge segments will occur. Such a situation is due to the different interaction in the structure of a bridge with supporting soil. Each bridge structure can respond differently leading to relative movements individually. The soil influence on period Ti in the bridge system can be found using the equation below[ CITATION Uni68 \l 1033 ];This where Ti has assumed fixed-base. The influence coming from the stiffness in vertical soil is set to be negligible. The actual situation is that soil stiffness is dependent on frequency thereby making the subsoil influence more complex. The equation and the diagram that is to follow indicate that even with both segments in a bridge having similar fixed-base in the fundamental period represented as T1 = T2 and similar ground support represented as k1x = k2x and k1Φ = k2Φ, a difference in height of structures will lead to a difference in system periods. Also, the bridge will react differently whether the ground excitation is similar or not[ CITATION Uni08 \l 1033 ]. Experiment.Lately, there has been a cope in thermal contraction and expansion in long bridges and extra Modular Expansion Joints are being used. The diagram below shows a two-segmented bridge with an MEJ.
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