Text Box:   Chairperson:  Chris Carroll, E.I. Virginia Tech jcarrol1@vt.edu 2007 Committee Report & Prioritized Wish List The Analysis and Design Committee has suggested several improvements as a result of committee discussions from the 2007 User’s Group meeting.  The suggested improvements were broken down into lists for both Analysis and Design and ranked in order of importance by committee members.  The prioritized list and corresponding descriptions are as follows. Analysis Design 1.    Base Plate Wizard 1.    True Tapered Beam Element 2.    Undo Button in GT Menu 2.    AISC 13th Edition 3.    Friction Element 3.    ASCE 7-05 Wind Load Calc. forBuildings 4.    Finite Element Mesh RefinementOption 4.    *Addition of ACI 318-05 5.    Calculation of Soil Pressure for Slabson Grade 5.    Code Check for Built-up CrossSections 6.    Cross Section Builder 6.    BCS Generate Taper Command with Nonlinear Capability for use in LRFD Code Checks 7.    Nonlinear Material for 2D and 3D FE’s 8.    *Multi Support Excitation 7.    AISC Code for Modular Construction *Currently being implemented in next version.             Analysis Detailed Descriptions Base Plate Wizard: A base plate analysis using GT STRUDL requires the user to construct a complete finite element model including: finite element mesh, compression only support springs, throughout the model, locations of anchor bolts, and the application of moments, axial and shear forces. This process can be tedious and require immense amounts of time to complete. A model wizard would be extremely useful in the design of base plates. The wizard would have a graphical interface with the following options: Shape (Rectangular/Circular) Dimensions (length, width, radius, thickness) Number of anchor bolts and pattern with coordinates provided by user Anchor bolt type, diameter, length, and embedment length Anchor bolt hole diameter Adjoining member Forces and moments in all directions Mesh size Based on this information, the wizard would then generate a finite element mesh including bolt-hole locations and take into account the connection of the adjoining member and the stiffness of the anchor bolt. Undo Button in GT Menu: When using GT Menu, users sometimes mistakenly change member properties, enter incorrect tolerances or improper mesh spacings. GT STRUDL does not currently have a way to correct for accidental modeling mistakes in GT Menu. Users are required to manually go back in and change member properties, completely re-mesh a boundary, or start over. The addition of an Undo button to the GT Menu features would be extremely useful. It should provide the option to go back at least to the model prior to the last command issued, and ideally have the ability to go back several steps.   Friction Element: When using the finite element features in GT STRUDL, some situations arise that call for compression only boundary conditions. In theses situations, especially with concrete, the shear resistance is based upon the contact friction between the layers of finite elements. This frictional resistance increases as the normal force increases, but there is currently no simple method for this modeling technique. Some cases have been modeled with a small gap placed in between layers of finite elements. The layers are then joined together with a combination of compression only members (springs) and multiple master and slave constraints placed between nodes corresponding to those joined with compression only members. The compression only members require a non-linear analysis. In addition to the non-linear analysis, the user is required to perform manual iterations as well. As compression only members go into tension, the user must release the shear transfer corresponding to the nodes adjoined to that compression only member. This process must continue until a reasonable convergence is reached. It is proposed by the committee that a friction element be introduced to the next version of GT STRUDL to facilitate this situation. The friction element should be able to incorporate the normal force transferred to one node to another and have capabilities for various coefficients of friction. This feature would be somewhat similar to the non-linear support springs already operational in current versions of GT STRUDL. Finite Element Mesh Refinement Option: GT STRUDL does not currently provide a means for finite element mesh refinement. The inability of GT STRUDL to provide such a feature has proven to be a hindrance when the finite element model mesh size is under question or when a model becomes too complex to generate using the CONSTRUCTION LINES/POINTS features in GT Menu. Implementing a feature in GT STRUDL that allows the user to easily establish and refine finite element meshes would prove quite useful.  Calculation of Soil Pressure for Slabs on Grade: When using finite elements to design slabs on grade, non-linear support springs are used to model the behavior of the soil beneath the slab. The stiffness of the springs is input by the user based on geotechnical reports or prior knowledge. The use of finite elements produces moment in the slab, but does not currently produce soil pressures resulting from loads applied directly to the slab. The committee suggests that an input be available for the user to specify an allowable bearing pressure for the soil and a warning message be given to the user in situations where the allowable bearing pressure of the soil is exceeded during the analysis. Cross Section Builder: The analysis of existing structures sometimes leads to discovery of miscellaneous cross-sections. In some instances, built-up sections are compiled of a number of different shapes. These members can be analyzed in GT STRUDL using prismatic members, where the user is required to specify all of the member properties. This procedure can be time consuming depending on the complexity of the structure and its structural members; it may also pose the possibility of member property miscalculations. A cross section builder would reduce the amount of time the user spends calculating member properties and exclude any possible miscalculations. The cross section builder would need to include a graphical interface allowing the user to place standard shapes and plates together, composing the desired built-up section. Each shape could be placed and rotated, if need be, based on its center of gravity. The composite properties would then be calculated by the program and stored in a database. The calculation of the member properties would be based on the assumption that there is sufficient connection of all shapes throughout the length of the member. Nonlinear Material for 2D and 3D Finite Elements: It is desirable in some situations to use a nonlinear material when doing a finite element analysis. Currently, GT STRUDL only allows the use of linear elastic material properties in such an analysis. For example, a nonlinear concrete material would allow the user to look at the redistribution of stresses due to cracking as well as crack propagation and possibly crack widths. This could be useful in the analysis of containment vessels as well as lock and dam systems.  Multi Support Excitation: The current version of GT STRUDL only allows for values of support excitation throughout the model. A multi support excitation option is currently being implemented in Version 29 which will allow the user to specify multiple excitations at various support points throughout the model. This option is only available when performing transient analysis. The committee recommends that this option also be available for other analysis options.   Design Detailed Descriptions  True Tapered Beam Element: The rationale for the true tapered beam element is to be able to model a tapered beam of tubular cross section with constant thickness. One possibility is to improve the BCS formulation of the GENERATE TAPER command for the user to input dimensions across flats as well as across points as it is now implemented. It is also desirable for the beam element to be used in a nonlinear analysis and code check per ASCE 48 (check only since a design would be impossible).  AISC 13th Edition: The American Institute of Steel Construction (AISC) introduced the 13th Edition of the Manual of Steel Construction in 2005. This edition encompasses both allowable stress design (ASD) and load resistance factor design (LRFD) into one single building code. It is vital to those using GT STRUDL in the design process to have this version of the code implemented into GT STRUDL.  ASCE 7-05 Wind Load Calculations for Buildings: Version 29 of GT STRUDL will have an antenna tower wizard that will have the option for wind load calculations. However, this is limited to antenna towers. The committee recommends an upgrade of the wind load calculation feature to also calculate building wind loads.  Addition of ACI 318-05: Starting on January 1, 2007, most states adopt the IBC 2006 which requires the use of ACI 318-05. Fortunately there are few differences between ACI 318-02 and the new ACI 318-05. In order to fulfill the requirements of the IBC 2006, it is essential that ACI 318-05 be available for use when using the design features in GT STRUDL.  Code Check for Built-up Cross Sections: As discussed in the analysis detailed descriptions, there is a great need for the simplification of the analysis of built-up cross sections. The implementation of a cross section builder would aid in the process of doing analysis. An additional aid in the analysis of built-up cross sections would be the possibility for code checks.  BCS Generate Taper Command with Nonlinear Capability for use in LRFD Code Checks: Currently in GT STRUDL, members generated by the BCS Generate Taper Command cannot be used in a nonlinear analysis run. It is important in the utility industry to do so in order to satisfy LRFD code check requirements for all other square tubes in the structure. The committee recommends that the BCS Generate Taper command be modified to be used in a nonlinear analysis.  AISC Code for Modular Construction: The development of GT STRUDL features that would accommodate the addition of the AISC Code for Modular Construction does not necessarily have precedence at the current time. The next generation of the nuclear industry will more than likely use this technology for its structures, so any consideration for future enhancements would be beneficial to the continued development of the program.