Changes for page Seismic analysis
Last modified by IwonaBudny on 2018/09/28 08:53
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... ... @@ 118,11 +118,11 @@ 118 118 == Dynamic calculations and Mass definitions == 119 119 120 120 (% style="textalign: justify;" %) 121  [[image:1536237300428654.pngheight="27" width="66"]]To calculate the seismic effect it is necessary to know the vibration shapes and corresponding periods, except the static method (lateral force method: linear force distribution). Therefore a dynamic calculation should be done before performing seismic calculation, which gives sufficient vibration shapes of the structure. To perform the dynamic calculation, it is necessary to define mass distribution which can be defined in Load tab as concentrated mass or load casemass conversion.121 +To calculate the seismic effect it is necessary to know the vibration shapes and corresponding periods, except the static method (lateral force method: linear force distribution). Therefore, a dynamic calculation should be done before performing seismic calculation, which gives sufficient vibration shapes of the structure. To perform the dynamic calculation, it is necessary to define mass distribution which can be defined in Load tab as concentrated mass or load casemass conversion. 122 122 123 According to EC8 3.2.4(2), mass distribution should be made in the following way: 123 +[[image:1536237300428654.pngheight="27" width="66"]] According to EC8 3.2.4(2), mass distribution should be made in the following way: 124 124 125 (% class="mark" %)ΣG ,,k,,,,,j,,"" + ""Σψ,,E, i,,Q,,k, i,,125 +(% class="mark" %)ΣGk, j"" + ""ΣψE, iQk, i 126 126 127 127 where: 128 128 ... ... @@ 130,6 +130,7 @@ 130 130 131 131 (% class="mark" %)ψ,,E, i ,,= ϕ ψ^^2, ^^i 132 132 133 + 133 133 The recommended values for ϕ are listed in EC8 Table 4.2. 134 134 135 135 The above formula means that mass conversation is made from all dead load without any factor, also masses in gravity direction temporary loads with reduced value. ... ... @@ 140,12 +140,14 @@ 140 140 (% style="textalign: justify;" %) 141 141 [[image:1536237268175179.pngheight="23" width="26"]] The program contains EC8 and NS349112 predefined design spectra or the user can define its own spectra if necessary. The vertical spectrum is necessary when the vertical affect taken into account. 142 142 143 === (% style="fontsize:18px" %)**EC8 design spectrum**(%%) === 144 +(% id="HEC8designspectrum" %) 145 +=== EC8 design spectrum === 144 144 145 145 The code gives the horizontal and vertical spectra and although the value of variables is prescribed, they can be modified if necessary. 146 146 147 147 [[image:1536237376815771.pngheight="247" width="315"]] 148 148 151 + 149 149 **Horizontal spectra** 150 150 151 151 Data of horizontal design spectra: ... ... @@ 183,11 +183,12 @@ 183 183 (% style="textalign: justify;" %) 184 184 In the Others tab, the user should set some parameters that effect the calculation and results. 185 185 186 * Ksi(ξ) 187 * qd 188 * Foundation level 189 +* Ksi(ξ) is the viscous damping ratio, expressed as a percentage, gene rally 5%. This data is used in modal analysis when the sum mation of the effect of the same direction vibration shapes is carried out by the CQC (Complete Quadratic Combination), see later. 190 +* qd is the displacement behavior factor, assumed equal to q unless otherwise specified. 191 +* Foundation level when Staticlinear shape is used, the program assumes that the foundation level is defined on that height. It means the pro gram calculates the mass height from that level. In the other two calculation methods (Staticmode shape and Modal analysis) base shear force is drawn in that level and it is taken into consideration in the so called reduced mass calculation (details in Effective mass setting). 189 189 190 === (% style="fontsize:18px" %)**NS349112 design spectrum**(%%) === 193 +(% id="HNS349112designspectrum" %) 194 +=== NS349112 design spectrum === 191 191 192 192 **Horizontal spectra** 193 193 ... ... @@ 208,6 +208,7 @@ 208 208 * S,,e,,(T,,i,,) is the acceleration for the period Ti in the normalized response spectra, see below, 209 209 * k,,f,spiss,, is a factor dependent on the reference period used. 210 210 215 + 211 211 **Vertical spectra** 212 212 213 213 [[image:1536238363669269.pngheight="32" width="119"]] ... ... @@ 223,6 +223,7 @@ 223 223 * k,,ν,, is the ratio between horizontal and vertical response spectra, mostly set to 0,7. 224 224 225 225 (% style="textalign: justify;" %) 231 + 226 226 The normalized response spectrum in Norwegian code is based on four different formulas, each covering a part of the possible periods from 0 to 4 seconds. Periods over 4 seconds has to be treated in a different way anyhow, and can therefore be based on a manually written response spectrum. 227 227 228 228 (% style="textalign: justify;" %) ... ... @@ 247,7 +247,8 @@ 247 247 248 248 In the NS349112 code only foundation level should be set. 249 249 250 === (% style="fontsize:18px" %)**Design spectra in the other national codes**(%%) === 256 +(% id="HDesignspectraintheothernationalcodes" %) 257 +=== Design spectra in the other national codes === 251 251 252 252 Except for the above mentioned two codes, the user has in all cases to define the spectra in table or in a graphical way. In the Others tab only the foundation level should be set. 253 253