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

STM Design Steps using CAST

The design using CAST can be summarized into five steps. They are illustrated in Figure 1 below.

Figure 1   Summary of Design Procedure Using CAST

Note that the steps are given here for guidance only; you do not have to strictly follow the steps in the order presented. For example, the first item in Step 1, i.e., Define Project Description, can be done in any step. However, some steps cannot be performed prior to the completion of related steps. For example, the Define Strut-and-Tie Model in Step 2 cannot be performed without the step Define Outer and Inner Boundaries being completed even though you still can modify the Outer and Inner Boundaries later. Another example is the step Define Strut, Tie, and Node Property Types in Step 4. This step cannot be completed without having information about concrete compressive and steel yield strengths defined in step Define D-Region Thickness and Material Strengths in Step 1. CAST implicitly notifies users of what the proper order of steps by three approaches:

• Enabling or disabling menus and buttons of toolbars associated with the current modeling process.
• Displaying dialog boxes that need to be completed before proceeding to the step you want to perform.
• Showing warning messages of improper order of steps in the status bar.

Credits:http://dankuchma.com/stm/CAST/procedure.htm

Current Features of CAST

Graphical User Interface
	Define D-Region boundaries graphically
	Define strut-and-tie models graphically and numerically
	Guidelines, grid points, and snap tools for accurate dimensioning
	Toolbars and dialog boxes for defining common elements, such as the imposed loadings, material properties, supports, and bearing plates
	Templates for common truss models
	Standard drawing and editing features, such as cut, copy, paste, delete, undo, redo, move, find, glue, and unglue
	Easy access to member information by mouse right button click
	Display of structural model, including reinforcement positions, labels, and areas, in multiple windows with various zooming and panning options
	Context sensitive online help
Analysis Types
	Design calculations (evaluation of truss member forces and truss member dimensions)
	Detailed analysis of nodal zones
	Simple truss capacity prediction
	Load-deformation analysis
Truss Solution
	Truss analysis and stress check at command
	Statically indeterminate trusses
	Truss stability checked with warning messages
	Illustration of member forces and identification of member characteristics for dimensioning
	Pushover analysis per user-defined stress-strain relationships of struts and ties with options to use load-controlled or displacement-controlled

Multiple Load Cases and/or Strut-and-tie Models
	Organize multiple load cases and/or strut-and-tie models in one database
	Present multiple load cases and/or strut-and-tie models in multiple windows
Truss Member Dimensioning
	Manual or automatic selection of effective widths of struts
	Single or multiple layers of tie reinforcement
	Checks of bearing plate stresses
	Quick check of the adequacy of strut-and-tie model components through color identification
	Support explicitly ACI Code requirements
Output Features
	Graphical and tabular output
	Create customized text input echo and/or output files
	Create design summaries including graphics in Microsoft Word Document format
	Create input echo and/or output tables in Microsoft Excel format
	Create graphics printout with print preview
	Export graphics into AutoCAD DXF and Bitmap files
	Create response quantity plots obtained from load-deformation analysis in Microsoft Excel format
	Display response history obtained from load-deformation analysis
Miscellaneous
	Support SI, US customary, and old metric units interchangeable during the design
	Support user-defined and ASTM Standard Reinforcing Bars (ASTM A615/A615M)
	Unit converter for helping convert physical quantities from one unit to another
	Built-in calculator for editable text boxes
	Customizable windows and toolbars

CAST: Computer Aided Strut-and-Tie

    The CAST program is being developed to provide both students and practitioners with a graphical design tool that makes the design process more efficient and transparent. The principal investigator of this research has had the opportunity to teach the STM to students at the University of Illinois since Fall 1997. It has been his experience that students readily take to STM due to their familiarity and confidence in the simple mechanics of a truss. They have also been able to grasp proposed design provisions for the strength of struts, ties, and nodal zones. However, once a specific design assignment is given, they can quickly become bogged down in the details of calculating truss member forces and ensuring that the dimensions of the struts and nodal zones are sufficient to support the imposed loadings.

The CAST program is a graphically interactive design tool that has been under development since Fall 1998 and has been used by students taking the second course of Reinforced Concrete Design at the University of Illinois since Fall 1999. The NSF CAREER is making possible the continued development of CAST. This will enable the growth into a program that allows designers to quickly optimize their design, handle multiple load cases, and generate final drawings. This program also serves as an instructional device, familiarizing students and practitioners with both the program and the strut-and-tie design philosophy.
CAST utilizes a single interface for creation or modification of strut-and-tie models, truss analysis, selection of reinforcing steel, and capacity checks of the struts and nodes. CAST was developed within Windows 32-bit environments. This means that it will only work on Windows 95/98/2000/ME/XP or NT 4.0 machines.

Credits: http://dankuchma.com/stm/CAST/