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This project primarily concentrates on the various concepts and innovative skills that required building the sketches and hence creating the 2D cad drawings along with the generation of the 3D models in AutoCAD. The engineering graphic has undergone many significant changes over the past decade through the application of several computer-based applications and the CAD and Revit software. Engineer from different backgrounds is usually found very essential in communicating and interpreting various design ideas by the use of several graphical-based approaches like model sketches and CAD-based drawings.
A truss bridge is generally a structure consisting of rigid material and made with different straight members such as the Beams, I section, Angle section, etc. The truss structure is usually the triangular-shaped type frame structure which would assist in the distribution of the various compression and their tension forces acting on different sections of the truss. The triangular structure provides the best approach to transferring the various loads as it gives stability to the truss structures since its geometrical shape is symmetrical and stable. Trusses are considered in the making of some of the b type structures by which the material could be used very effectively and efficiently (Crifasi, Et al. 2020). In the bridges, some series of different beams and trusses have been used widely rather than using single beam structures to withstand the different forces. Many truss bridges have been used nowadays but the primary purpose is the same for all truss bridges to distribute the tension and the compressive forces for which the bridges should not collapse. The trusses having a 3D structure are analyzed by assuming it to be a planar structure. For the designing of a truss, it is essential to determine the several forces acting on each of the members.
The assumption that has been provided below is considered while the design of the truss bridge has proceeded and the determination of the tension forces along with the different compression forces have been addressed.
The different members of the bridge are classified as chord members and some web-type members (Delaney and Jurgenson, 2019). The function of chord members is to control and resist the entire bending moment that is acting on the bridges mainly in the different firms such as the axial tension, and the axial compressions. While the web members must carry the various shear forces that are acting in the form of directly tensioned and direct compressions.
Therefore considering trier efficiencies this truss bridge is classily built on the wide ranges of the bridge's spans. The truss bridges are mostly completed against the various plate girders for the short spans but the box girders used for the medium-based spans and the long spans must be used for the longer cable-type bridges. For the medium spans, it would be economical hence warren trusses have been used in the category of parallel-based chord trusses (Sharma et al. 2020). The Pratt truss and howe truss are mainly used for the minimization of the fabrications along with the various erection costs. Moreover, the longer spans are required to make a certain high depth mainly at their center and should use the concept of variable depth of trusses so that it could be adopted for the primary purpose of economic bridges. As in this project, the truss depth is generally larger at their supports, and the mid-spans have a smaller depth (Kromoser et al. 2020). The diagonal members must be placed at an angle of 60 degrees from the horizontal. The secondary type stresses are to be avoided to ensure that various centroidal-based axes for all the various interpreting members must be able to meet at the provided single points.
The design principles include the information regarding the optimum depth provided in the truss girders. The optimum based values for the given span to depth-based ratios mainly rely on the different magnitude of the generating live loads. This span depth ratio for the truss bridge develops the great economy for the material that has been used that would make the various weights of the chord members equal to provide the weight of the different web type members of the bridge trusses (Dutta, 2022). The value must be in the range of 10, which would be higher for the traffic on roads as compared with the rails. But as per the rules provided by the railway bridge board, bridge depth must not be larger than 3 times of width that is considered between the centers of reference girders. The truss spacing would depend on the clearances that are needed to provide on the railway and roadway bridges.
Design of chord members of compression
The Buckling of respective compression members are depending upon the effective length which rarely occurs in-plane and it is not the same as the out-plane truss buckling. This shows that truss members become weak in one of the given as compared to the out plane. The best vans ideal members of chord members would be the section that has the radius of gyration so that their slenderness ratio would be similar in both of the planes. In addition to that members would try to buckle in the direction of the in-plane and corresponding out plane. The primary objective is to make the members short and the various considerations would be provided mainly to the bracing part so that the overall structure becomes economical (Melaragno, 2021). The factors related to effective length in the category of compression of the truss members are evaluated by the stability analysis method. The member's depth is so chosen to maintain the various plate dimensions in their reasonable manners. For thick members, the radius of the gyration would become smaller if a similar quantity of steel is used to make the formation of large members by the application of thin plates. These plates should be thin as much as possible but not lose their area while the effective member's section would derive and not become much vulnerable to the corresponding buckling.
In the above figure, there is a representation of the shaded with edges view of the designed truss brides on AutoCAD software. The wireframe structural view has been shown in the figure.
In the above figure, there is a representation of the elevation view of the truss bridge that is designed on Auto-cad software. The connection used in the bridges is a bolted connection and it has two major supports. The bridge has been designed by assuming the total span of the bridge is 10m and its width provided as 3.5m. The structure is made symmetrical so that the various loading conditions should be proper manner and provide stability efficiently and effectively.
In the above figure, there is a representation of a 3d realistic view of the designed truss bridge. This process proceeds with the 2D drawings and then extrusion of the model carried out in the Auto-cad to obtain the desired structure.
The conceptual model view is shown of the truss bridge that has been designed on AutoCAD by considering the span of 10m and width of 3.5m. In this way, different views of the given bridge could be obtained on AutoCAD and Revit modeling software.
Design of Tension chord members
The tension members must be compact as much as possible since their depth must have to be sufficiently high to give enough space mainly for the various bolts primarily at their gusset plates and should attach them easily at the cross beams (English and King, 2019). The weight-related to the out plane for the bridge truss must be similar to that of the various vertical members and also to the diagonals to make the allowances of the gusset properly without the requirement of packing. This should be achieved by the precise arrangement of the various bolts along the splices producing an effective 85% of the total sectional area.
In the above figure, a different type of cross-section that is commonly used in the design of bridges is shown. The section considered in this project for design is the Built-up I section which is more economical and stable as well.
Design procedure for vertical and diagonal type members
These sections are often referred to as the rolled sections as they are considered the light loading members since the packing would be needed mainly for preparing the rolling margins. Through this approach, the various welded members would become more economical but significant on the longest spans trusses in which the operation related to the packing would raise the erection cost of the members (Jiang, 2021). As far as the aesthetic view of the bridge is concerned, the member lying on the diagonal must be kept at a similar angle even if the different chords are not present along the parallel way. This type of arrangement would help in the prevention of the over-complexity view while the bridge viewed from a prescribed angle. The different types of crosses that have been used in the design are shown above figure to provide a better understanding.
Lateral bracing designs
The lateral bracing system provided to the truss bridges is mainly for the transmission of the various live loads along with the several lateral loads acting on the bearing to prevent the various compression of truss members from buckling. This could be done by the proper placing of the stringer bracings, their girders, and also the various chord members of lateral bracings. But in the special case of the road bridges, the concrete decking system would also be acted as the lateral bracing and support as well
The above figure gives the lateral bracing systems that have been used these days in the construction of truss bridges whether it's highway or railway-based bridge. The deformed shape and St Andrews cross-system of lateral baking is shown here.
The nodes corresponding to the lateral system coincide mainly with the different nodes of primary trusses. Apart from the design and site investigation, using the analytical approach is also used mainly in the calculator of structural failure and its deterioration. The various formulas and different software design procedures have been followed to obtain desired results. The plant-based management cycle is the tool to ensure the tracking process of bridge design, their serviceability, and also durability for a longer time during material deterioration by the aging process. The techniques such as their visual inspection, destructive type testing, and the various analytical methods followed. The detailed design must follow the respective code for their durability and according to the structural model that is given in the code.
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