AASHTO Spectrum Calculation

Current spectrum calculation method is not correct for AASHTO. See implementation in origin source code. Note, the primary difference in how sPGA is computed. Also note, the spectrum should be extended to T = 4.0 s rather than depending on T_L (which is not considered in AASHTO). Original Java implementation for reference:

 /**
   *
   * @param saVals ArbitrarilyDiscretizedFunc
   * @param fa float
   * @param fv float
   * @return DiscretizedFuncList
   */
  public XY_DataSetList calculateSDSpectrumForAASHTO(ArbitrarilyDiscretizedFunc
                                                 saVals,
                                                 float fa, float fv, float fpga,
                                                 String siteClass, String edition) {
    double tAcc = saVals.getX(0);
    double sAcc = fa * saVals.getY(0);
    double sVel = fv * saVals.getY(1);
    double sPGA = fpga * saVals.getY(8);

    XY_DataSetList funcList = approxSaSd(tAcc, sAcc, sVel, sPGA);

    saTfunction.setName(GlobalConstants.DESIGN_SPECTRUM_SA_Vs_T_GRAPH);
    saSdfunction.setName(GlobalConstants.DESIGN_SPECTRUM_SD_Vs_T_GRAPH);

    String title = "Design Response Spectrum for " + siteClass;
    String subTitle = "SDs = Fa x Ss and SD1 = Fv x S1";

    String info = "";
    info += title + "\n";
	info +=
		DataDisplayFormatter.createFunctionInfoString(funcList, siteClass, true);
    funcList.setInfo(info);

    return funcList;
  }