====== SITE Module Options ====== {{ :sassi:user_interface:siteopt.png |}} The ACS SASSI [[sassi:SITE]] module has two basic operation modes: - Form and solve transmitting boundary eigenvalue problem - Mode1 - Solve the site response problem - Mode 2 **Mode 1:** The ACS SASSI SITE module reads the soil layer properties and for each specified frequency forms the transmitting boundary submatrices for Rayleigh and Love wave cases. Then it solves the two eigenvalue problems, as described in the Theoretical Manual, from which the eigenvalues and eigenvectors of the soil layering are obtained. The results are then written to File2. The halfspace condition is also simulated at this stage. ACS SASSI SITE automatically generates a specified set of sublayers whose thickness vary with frequency attached to viscous dashpots at the base. The generated sublayers and dashpots are then added to the fixed top layers. File 2 provides the information needed to run ACS SASSI [[sassi:SITE]] in Mode 2 as well as to compute the transmitting boundary by ACS SASSI [[sassi:POINT]]. Since the eigenvalue problems to be solved for an arbitrary three-dimensional horizontally layered site are the same as those to be solved for a plain strain model, the information from File2 can be used for both two- and three-dimensional cases as well. **Mode 2:** The ACS SASSI SITE module recovers the soil layer properties and the eigen solutions for Rayleigh and Love wave cases from File2. Then, according to the existence of each wave type, ACS SASSI SITE computes the mode shapes and wave numbers for each wave type in the defined coordinate system. Then, once the composition of the wave types causing the seismic environment and the nature of the control motion is known, ACS SASSI SITE will scale and superimpose the results of all the wave types. These results are then stored in File1, which is used later for seismic analysis. Thus, this file will not be generated for foundation vibration analysis. If the seismic environment is the same for a two- and three-dimensional case, the information from File1 can be used for both problems. The following options allow you to specify the analysis options for ACS SASSI SITE module: * **Operation Mode** - Select the operation mode from Linear Soil and Non-linear Soil. This selection will generate a linear or a non-linear SSI analysis (only primary soil nonlinearity is included). NOTE: If Non-linear Soil option is selected then the dimension for the soil input data for SITE and SOIL should be consistent either in BS or IS of unties (kip, ft, ksf, kcf or kN, m, kN/m2, kN/m3). The check boxes Mode1 and Mode2 enable/disable the two basic operation modes of module SITE. * **Acceleration of Gravity** - Type the acceleration of gravity in ft/sec2 for BS, or m/sec2 for IS. This acceleration of gravity value is used for SSI analysis. A change of this value does not affect the value used for free-field analysis in SOIL options. * **Frequency Step** - Type the frequency step %%(Hz)%%. * **Time Step of Control Motion** - Type the time step of control motion %%(sec)%%. * **Nr. of Fourier Components** - Type the number of values to be used in the Fourier transform. The value should be a power of 2, otherwise ACS SASSI PREP uses the closest power of 2 and generates a warning message. For a time history analysis, the time step and number of Fourier components for the selected time history of the control motion must both be defined, and the frequency step may be left blank. ACS SASSI SITE computes the corresponding frequency step = 1 / (time step * number of Fourier components) . This frequency step may then be used to set up the frequency numbers in the specified frequency set. For a single harmonic analysis the frequency step must be given and may be directly used to set up frequency numbers in the specified frequency set. In this case, the time step of control motion and the number of Fourier components are not used and therefore may be left blank. * **Frequency Set Number** - Type the number of the frequency set created with the [[com:FREQ]] instruction. The frequency numbers from the specified set must be positive integer numbers. ACS SASSI SITE will automatically reorder the frequency numbers in ascending order and will stop if two or more equal frequency numbers are detected. The frequencies are obtained by multiplying the frequency number by the frequency step. * **Number of Generated Layers** (used for half-space simulation)- Type the number generated layers to simulate a half-space (between 4 and 20). Leave this edit box blank (or type 0) if you wish to suppress the half-space simulation. If the half-space simulation is suppressed, the soil profile will be assumed on rigid base; otherwise a specified number of sublayers whose thickness varies with frequency are generated to simulate the half-space. Also, ACS SASSI SITE will add viscous boundary to account for radiation damping in the halfspace through the lower boundary. Using the value 10 is recommended for halfspace simulation. * **Half-Space Layer** - Type the number of the soil layer property associated with the half-space or baserock properties (see [[com:L]] command. * **Top Layers** (define the free-field soil layering above half-space / baserock) - Type a list containing the numbers of the soil layers (created with the [[com:L]] command ) defining the soil structure. The allowed separators are blank, tab, ‘,’, ‘;’, and enter. The maximum number of soil layer numbers is 100. The first number corresponds to the topmost layer. To view the soil layers, select the [[sassi:user_interface:soil layers|Plot / Layers]] command. Tip: If two or more top layers have the same properties, simply use the same soil layer number instead of defining soil layers with the same properties. Soil properties should be consistent in SOIL and SITE modules if non-linear SSI analysis is performed. * **R-, SV-, and P-Waves** - Select this option if your model uses a combination of P-, SV-, and R-waves (use for 1D and 3D analyses). * **SH- and L-Waves** - Select this option if your model uses a combination of SH-, and L-waves (use for 1D and 3D analyses). The seismic environment may be assumed to consist of one single wave type or several wave types. The basic wave types are P-waves and S-waves, which are also called body waves. When these waves impinge on the ground surface or layer interfaces, surface waves which include R-waves and L-waves may be generated. P-waves involve motions in the direction of wave propagation. S-waves involve motions perpendicular to the direction of wave propagation. S-wave motions in the vertical plane are called SV-waves. Horizontal S-waves are called SH-waves. R-waves involve horizontally propagating elliptical motions in the vertical plane and L-waves consist of horizontal motions perpendicular to the horizontal direction of wave propagation. With the above definitions, ACS SASSI SITE sets up a coordinate system so that P-waves, SV-waves, and R-waves involve particle displacements in the x’z’ plane while SH-waves and L-waves involve particle displacements along the y’ axis. Therefore, the z’ axis is always vertical up, x’ is in the vertical plane of wave propagation, and y’ is perpendicular to x’ and z’ following the right-hand rule. {{ :sassi:user_interface:options:waveprop.png |Wave propagation and associated parameters}} * **R-Wave** - Select this page to set the R-wave field options - choose between No R-Wave Field, Shortest Wavelength, and Least Decay. * **SV-Wave** - Select this page to set the SV-wave field options - choose between No SV-Wave Field, SV-Wave Field. * **P-Wave** - Select this page to set the P-wave field options - choose between No P-Wave Field, P-Wave Field. * **SH-Wave** - Select this page to set the SH-wave field options - choose between No SH-Wave Field, SH-Wave Field. * **L-Wave** - Select this page to set the L-wave field options - choose between No L-Wave Field, L-Wave Field. * **Wave Ratio 1** -Type the wave ratio for the selected wave type at the first frequency. * **Wave Ratio 2** - Type the wave ratio for the selected wave type at the second frequency. In the case of seismic environment composed of two or more wave types, the ratio of participation of each wave type must be given. This ratio in general may be frequency-dependent and is defined at two discrete frequencies for each wave type. These frequencies must cover the frequency range of analysis. The ratio values for intermediate frequencies will be obtained by simple interpolation and therefore need not be given at exact frequencies for which complete solution is required. In the case of seismic environments consisting of one simple wave type, the two frequencies (one in the beginning and the other at the end of the frequency range of analysis) with assigned ratio values of 1 are enough to define the ratio curve. All ratio values are positive decimal numbers less than or equal to 1, and the addition of the ratio values of all the participating wave types at each frequency must be 1. * **Incident Angle** - Type the incident angle of the selected wave type. The incident angle is defined as the angle between the direction of propagation and the z’ axis. For vertically propagating waves, this angle is zero. * **Frequency 1** - Type the first frequency to define ratio curve. * **Frequency 2** - Type the second frequency to define ratio curve. * **Control Point Layer** - Type the layer number of the control point. The control point is defined as the point where the control motion is specified. It will be located at the top of the specified layer number, e.g. 1 for the control point at the surface. * **Direction** - Select the direction of the control motion in the x’y’z’ coordinate system. The transformation of the coordinates from the x’y’z’ system to the final xyz coordinate system of soil structure will be done by the ACS SASSI ANALYS module.