Table of Contents
Abstract
The current research majorly focused on exploring different aspects related to bridge construction where what is required during bridge construction, bridge loads and type of forces exerted on bridges were looked into. Specifically, the study focused on understanding the forces exerted on different types of bridges in terms of bridge construction and they include compression, tension, torsion and shear. The study also aimed at understanding how the torque (torsional) and shear strain gauges are connected in measuring the strain in a twisting object. It is proposed that a full bridge connection can be influenced optimally by the load where increase in the load weight leads to increase in the strain and gauge factor output relative to the increase in the bridge set up. This study clearly indicated why it is important for engineers to put different aspects related to bridge constructions into consideration when designing and constructing bridges.
Introduction
There has been tremendous advancement in bridge construction in terms of science and technology. In this case, lighter and much better materials have been considered where they have a capacity of enduring heavy loads. This implies that the process of construction is faster as a result of using heavy equipment. In bridge construction process entails utilizing different skills associated with engineering disciplines such as computer science, mechanical, electrical, civil and geology. This means all these should be integrated in the bridge construction process in meticulous manner (Stokes, 2001). The initial plans of bridge construction entails consideration of the resources required, site details, desired bridge characteristics. The design of the bridge is always based on the type of bridge to be constructed. There are different types of bridges and the main ones include suspension, cantilever, truss, arch and beam. The most popular bridge is considered to be Beam Bridge (Stokes, 2001). The classification of the bridges can as well be based on the type of material used such as steel or concrete, pedestrian pavement, rail bridge etc.
The goal of this study was to explore different requirements in building bridges. In this case, it is pertinent to first explore different forces exerted on bridges. Bridges are required to withstand different kinds of forces. The most considered types of forces in bridge modeling include pulling and pushing and tension and compression respectively. Shear and torsion (twisting) are the other types of forces considered. In this case, these forces have been explored as in the next section.
Compression
It can be defined as a pushing force. For instance, the length of the piece of wood is proportional to its compression and this means that longer wood pieces are able to hold less compression. Another example is that when a long stick is compressed, it will start to bend and in cases where the wood piece breaks as a result of compression it can be referred to as “failed from buckling.” The bridge’s top chord that includes model bridges is considered to be in compression (Troyano, 2002). Various designs of truss are seen to spread out to enable different internal parts to be in compression.
Tension
It can be defined as a pulling force. Wood has been found to have a capacity of resisting high amounts of tension. For instance, it is not easy breaking a Popsicle stick if both ends are held and then pulled apart. The application of tension could be parallel to the wood grain and thus, perpendicular to the wood grain needs to be avoided (Troyano, 2002). In this respect, parallel to the wood grain application is associated with a stronger tension and on the other hand, perpendicular to the wood grain application is associated with weaker tension (Troyano, 2002). Contrary to compression, the wood length is not affected by tension resistance capacity of the wood. This implies that the tension amount held by a longer wood piece is the same as that of the shorter wood piece.
Torsion
It can be defined as a twisting force. For instance, in wringing out a cloth, a torsion force is applied. A stick pretzel is able to break easily when its one end is twisted while the other end being held. The breakage won’t be observed when this is done on a baseball bat. The bridge’s steel sections are considered to be resistance to torsion. The moving vehicles forces are seen to exert torsion to a given bridge deck. Strong winds have as well been seen to exert torsion to a given deck (Troyano, 2002). The bridge designers are therefore required to pay much attention when it comes to torsion where it should be reduced as much as possible.
Shear
It is considered to be stress and it entails two opposite forces seen to act at the same point. For instance, a skinned knee is associated with shear. If two wood pieces are held next to each other and then pushed in an upward and downward direction, the force being applied will be shear. The application of shear is normally horizontally, but not vertically. Moving water and wind could lead to shear stress. The grounds anchoring the bridges can shear as a result of earthquakes and hence, some sections of the bridge could shear (Troyano, 2002).
Bridge loads
There are different types of loads known to act on a given bridge and as such, dynamic loads are seen to be of significance. A bridge is designed in a special way where it is able to endure vehicle loads as well as other forces generated as a result of earthquakes and winds. Strong winds have been reported to cause a collapse of many bridges. There is always failure by the bridge to resist the dynamic forces caused by the wind regardless of the wind speed (Espinosa, 2007). The bridge normally vibrates vigorously initially and this leads the structure of the bridge to fail and thus, the major bridge components could be damaged. Based on several studies, it has been found that after bridge failures the actual forces exerted on the bridges were seen to be less than the loads meant for the bridge. The generated oscillations however were as a result of winds associated with failure.
Truss
Truss enables structure analysis based on the several assumptions as well as on Newton’s laws of motion relative to the static. Truss is considered to be a pin joint with components straight in nature. There are different types of truss and they include chords where diagonal and vertical ones usually act in a compression or tension basis. When a load is subjected to a rigid joint there is need of undertaking a more complex analysis.
Truss is applicable in the construction industry where different products are designed for every given development. The bridges made from truss consist of connected elements stressed from compression and tension based on dynamic loads (Beer et al. 2002). Bridges made out of truss are considered to be economical in terms of construction. The frames of trusses consist of timber joined by bolt, nails for the purposes of strength enhancement and stability. The truss that is statically indeterminate is applicable in the construction industry and the built structures are able to withstand different conditions such as failure of nails holding the frames together. Statically indeterminate truss is applicable in designing of bridges or truss (Giancoli 2008).
Strain measurement
Strain is defined as the body’s deformation level as a result of the force applied. Specifically, it can be defined as the change in fractional length. Strain can either be negative or positive (Budynas et al., 51). There are various methods of strain measurement, but the frequently used is strain gauge and it is a device that has electrical resistance that varies relative to the strain amount in the device. Piezoresitive gauge for instance is a device that is semiconductor where its resistance variation relative to strain is nonlinear (Fessler et al., 35). Bonded metallic strain gauge however is considered to be a gauge that is frequently used. Practically, strain measurement in the measurement of strain gauge rarely entail amounts larger than a given few mil-strain. Thus, the measurement of strain needs accurate measurement of resistance in terms of small changes. For such small changes to be measured in resistance there is need to employ a bridge configuration with a current or voltage source. In this experiment, the bridge used consisted of four resistive arms that have excitation voltage applied across a given bridge. When two strain gauges are used in the bridge, the temperature effect is seen to be avoided (Budynas et al., 34). This therefore means that the effect of strain on the second gauge is very minimal. Any temperature changes observed will have an effect on the gauges in the same manner (Budynas et al., 41). Due to the fact that in both gauges, changes in temperature is same the resistance ratio is seen not to change and as such, there is no change in voltage as well as the temperature change effects are reduced.
Conclusion
The four stresses discussed can be managed by different bridge types in various ways. Every bridge type has the capacity of withstanding a given optimal stress. This is helpful to engineers where they are able to choose the kind of bridge to be build based on a given specifications. Compression and tension of bridge deck can be managed by the bridge designers in two ways. Spreading a given forces a cross a given beam in an even manner is one of these ways. Devices like girders and trusses helps in achieving this process. Force transfer to another structure is considered to be the second way. In this case, suspension bridge towers are some of the examples where compression and tension has been transferred to other structures from the bridge deck. The suspension bridge deck can exhibit relatively low tension and compression. This is based on the fact that the bridge deck is held together by many cables. Wind in this case is seen to cause torsional stress exhibited on such bridges. In this case, trusses are normally added by engineers and this critical in stabilizing the bridge. The stability of the bridge can as well be increased if a diagonal suspender cables are added. Shearing stress is exhibited following the twisting of the object and at the same moment there is compression and tensile stress exhibited. It is proposed that torque (torsional) and shear strain gauges are connected in measuring the strain in a twisting object.
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