STAAD Pro Advanced Analysis

STAAD.pro 2007 Advanced Analysis Option

By

RAM/STAAD Solution Center

19 December 2007

The Advanced Analysis Module includes the four major features: 1. Pushover Analysis 2. Steady State Analysis 3. Advanced Solver; and 4. Buckling Load Analysis 1. Pushover Analysis: Pushover Analysis option will allow engineers to perform pushover analysis as per FEMA 356 : 2000 and ATC 40. Pushover analysis is a static, nonlinear procedure using simplified nonlinear technique to estimate seismic structural deformations. It is an incremental static analysis used to determine the forcedisplacement relationship, or the capacity curve, for a structure or structural element.

Figure 1: Capacity Curve for a Structure in STAAD.pro 2006 Pushover Tab The analysis involves applying horizontal loads, in a prescribed pattern, to the structure incrementally, i.e. pushing the structure and plotting the total applied shear force and associated lateral displacement at each increment, until the structure or collapse condition. An example of the capacity curve is shown in Figure1. The displacement diagram after 225 steps and the location of plastic hinges at the 11th step is shown in Figure 3 and 4 respectively.

Figure 2: Node displacements at Step 220 in STAAD.pro 2006 Pushover Tab

Figure 3: Location of Plastic Hinges in STAAD.pro 2006 Pushover Tab

In the current implementation of the pushover analysis, the user can provide hinge properties as per Table 5-6 and 5-7 of the FEMA 356 manual (Generalized Force-Deformation Relationship) and also enter the expected yield stress of steel.

Figure 4: Hinge properties can be defined in the Loads tab in the modeling mode STAAD.pro's pushover analysis is currently only applicable to steel structures. 2. Steady State Analysis: A structure [subjected only to harmonic loading, all at a given forcing frequency and with non-zero damping] will reach a steady state of vibration that will repeat every forcing cycle. This steady state response can be computed without calculating the transient time history response prior to the steady state condition. Ground motion or a joint force distribution may be specified. Each global direction may be at a different phase angle. Output frequency points are selected automatically for modal frequencies and for a set number of frequencies between modal frequencies. There is an option to change the number of points between frequencies and an option to add frequencies to the list of output frequencies.

Figure 5: Steady state analysis inputs in the STAAD.pro input file

Figure 6: Steady state analysis outputs

The results are the steady-state response which is the absolute maximum of displacement (and other output quantities) and the corresponding phase angle after the steady state condition has been reached. In addition, a Harmonic response can be calculated. This response consists of a series of Steady State responses for a list of frequencies. The joint displacement, velocity, or acceleration can be displayed as the response value versus frequency. Load case results are the maximums over all of the frequencies.

Figure 6: Steady state analysis outputs – Displacement vs. Frequency charts 3. Advanced Solver: In the STAAD.pro 2007 the user will have three types of solvers: 1. Basic out-of-Core 2. VKI out-of-Core; and 3. VKI in-core • • • • • • •

VKI solver will be available as part of the Advanced Analysis option VKI in-core solver will be used for models with under 20,000 joints VKI out-of-core solver for models over 20000 joints The VKI in-core solver is 500 to 2,000 times faster than the STAAD solver The VKI out-of-core solver is between 50% and 100% as fast as the VKI in-core solver VKI solver is also good for dynamic analysis, master/slave models, and models requiring iterative solutions.

4. Buckling Load Analysis: STAAD.Pro can now identify the factor by which the loads in the selected load case should be increased (or decreased if less than 1) such that Euler buckling would occur. This buckling method is automatically activated if an Advanced Analysis license is available. When using the Advanced Solver, the corresponding ‘buckling modes’ are included in the output file. The buckling modes and shapes and table are available to be viewed in the Post Processing Mode in a new Buckling Page.

Figure 7: Buckling Mode Table

Figure 8: Buckling Mode Factor