Double Corbel Design using CAST (Part 2)

 

 In the above figure, STM shape that is adopted for design the double corbel is shown. To illustrate in more details all components of this STM constructed by CAST, the following info is provided below.

• D-Region Boundary:
  • A closed, non-intersecting polygon that defines the geometry of the structure.
  • There are two types of D-Region Boundaries: Outer Boundary (Perimeter) and Inner Boundary (for openings).
  • You are allowed to create only one Outer Boundary, but you can create as many Inner Boundaries as you want.
  • Because there is only one Outer Boundary that should exist in your model and the region inside the Outer Boundary represents the concrete continuum, you are not allowed to copy, cut, or remove it from your model once you create it. However, you are surely allowed to change the positions of the Boundary Corners. You are also allowed to add and remove Boundary Corners as you wish.
• D-Region Boundary Corner:
  • Intersection of two Boundary Edges.
• D-Region Boundary Edge:
  • Line connecting two Boundary Corners.
  • Place for STM Nodes that possess Bearing Plates, Point Loads, or Point Supports.
• Strut-and-Tie Model:
  • Internal truss in the D-Region.
  • Consists of STM Elements interconnected at STM Nodes.
• STM Element:
  • Component of Strut-and-Tie Model.
  • STM Elements can be in the form of Struts (compressive STM Elements) or Ties (tensile STM Elements).
  • STM Elements have Effective Widths, representing the extent of idealized compressive stress fields (for Struts) or tensile stress fields (for Ties).
• STM Node:
  • Component of Strut-and-Tie Model.
  • Place where one or more STM Elements meet, also called a nodal zone.
  • There is only one STM Element allowed to frame into an STM Node having Bearing Plates, Point Loads, or Point Supports.
• Stabilizer:
  • STM Element whose member force is zero.
  • Stabilizers are not included in the nodal zone construction.
  • Stabilizers are required to avoid ill-conditioned structure stiffness matrix in truss analysis.
  • You must always create a stable Strut-and-Tie Model; Stabilizers are identified by CAST during truss analysis.
  
  
  After you are familiar with all components given above, it is time to show you steps by steps how to construct STM using CAST. Please follow the instruction in the next post. For the previous post about designing of double corbel using CAST (part1) please see here.
  
  

Double Corbel Design using CAST (Part 1)

Overview

In this document, the task of designing a double corbel is completed to illustrate how the CAST Design Tool (Version 0.9.10) can be used for the design of D- (Discontinuity) Regions. Following a brief introduction and description of the CAST graphical user interface, a step-by-step solution is presented. In order to describe many of the important features of this program, complete details are provided with associated images from CAST. The completion of this exercise and thus familiarization with CAST is estimated to take 60 minutes.

Introduction

Figure 1 describes the geometry and loadings for the double corbel structure being considered. The thickness of the corbel is 600 mm. The concrete strength is 35 MPa, and the yield strength of reinforcement is taken as 420 MPa. The corbel supports an ultimate vertical force of 1000 kN and an ultimate horizontal force of 100 kN at each end and two ultimate point loads of 3000 kN in the supporting column region. Bearing plates of 150 mm length x 600 mm width x 25 mm thick are provided at each end of the corbel. Figure 2 shows the selected strut-and-tie model for this structure. The design will be completed to meet ACI 318-02 Appendix A requirements. Figure 1   The Geometry and the Loadings of the Corbel under Consideration Figure 2   Strut-and-Tie Model Employed in this Corbel Design