Introduction Tower cranes are a common fixture at any major construction site. They often rise hundreds of feet into the air, and can reach out just as far. Tower cranes are used to lift steel, concrete, large tools like acetylene torches and generators, and a wide variety of other building materials.
Arm and Tower Sections Jib section Tower Section
Dimensions The tower crane is approximately 120m tall 10m wide The counter weighted arm is 60m long And the main jib can be as long as 90m
Modelled Tower Crane Looked at 2 scenarios 2d 2d 3d 3d The aim was to determine the differences in both 2D and 3D cases in relation to displacement and stress analysis
Objectives To use Strand 7 on a complicated structure such as a tower crane Model the tower crane to the dimensions given from relevant data Determine stresses and displacements associated from various locations of loads on the structure Try and improve the structure
Objectives To see if there was a better way of modelling the tower crane on Strand 7 Through using different materials Through using different materials Modifying the shape Modifying the shape
Method Determined the dimensions of the tower crane using data from the internet and other relevant crane construction guides Determined various components involved in the tower crane Identified the materials for each of the various components and then selected these from the strand 7 library
Method Drew a 2D representation of the tower then the arm and then used strand 7 commands to convert into a 3D structure Entered various loading scenarios Ran analysis Modified the elements accordingly to meet acceptable limits in the results.
Materials The materials used were predominantly structural steel of various sizes The cable also is made from steel with a free length ranging from 50 to 80m All sections are circular hollow sections
Load Cases Taken a variety of load cases Loads were placed at individual nodes along the arm of the tower crane In the final report the natural frequency is also going to be considered but hasnt been included now due to time constraints
Simplifications The main simplifications were: Simplifying the concrete counterweights into a few point loads Simplifying the concrete counterweights into a few point loads Not having a pivoting base. I.e. the nodes at the bottom of the tower are fixed in all directions and rotations Not having a pivoting base. I.e. the nodes at the bottom of the tower are fixed in all directions and rotations The 3d case didnt incorporate the service crane and the extra cables The 3d case didnt incorporate the service crane and the extra cables
Displacement Analysis 1 ST Case load at the end of the jib Maximum displacement 1.5m Loads : counterweight = 3x 30kN Jib =150kN
Displacement Analysis 3D Load case 2 : Maximum Displacement 0.41m Loads : counterweight = 4x 20kN Jib =150kN
Displacement Analysis 3D Third Load Case : Maximum Displacement 0.6m Loads : counterweight = 4x 20kN Jib =150kN
Displacement Analysis The 2 and 3D cases give quite similar displacements Up to 1.5m depending on the loads applied The worst case is when the load is applied at the end of the jib, which is what is to be expected.
Stress Analysis The stresses observed are not realistic ie. In the thousands of MPa This result is evident in all of the load cases
Stress Analysis In all cases the stress is beyond the yield strength of the steel used. Therefore there are errors that need to be corrected. This will be done by making the critical tension members solid and looking at the weights of each member.
Errors The main errors involved so far have been in relation to the units associated with the loads applied to the structure. The high stress involved may be due to the weight of the structure as a whole. Initially we were faced with problems relating to the stiffness matrix K. This involved, free or unconnected elements and also defining an element more than once in the same position.
Modifications Main modification factors are : Modifying the cross-sections of some members to decrease the high stresses observed Modifying the cross-sections of some members to decrease the high stresses observed Wind load scenario Wind load scenario Natural frequency analysis Natural frequency analysis Seeing the effect of other materials and how they affect the results. Seeing the effect of other materials and how they affect the results.