where is the error, why speudo velocity spectrum graph not coming pls help.

%% Elastic Response Spectra
% This function generates elastic response specra including Displacement
% Spectrum, Pseudo Acceleration Spectrum, and Pseudo Velocity Spectrum which
% are needed in a "Response Spectrum Analysis" of structures. To solve 
% the "equation of motions" for different periods, the Newmark Linear Method 
% was used. 

%% SPEC Function Help:

% INPUT:
% dt:     Time Interval (Sampling rate) of the Ground Motion
% Ag:     Ground Motion Acceleration in the unit of the "acceleration", e.g. m/s^2  
% zet:    Damping Ratio in percent (%); e.g. 5
% g:      Gravitational Constant; e.g. 9.81 m/s^2; g determines the output unit
% endp:   End Period of the Spectra; e.g. 4 sec.

% OUTPUT:
% T:      Period of the Structure (sec.)
% Spa:    Elastic Pseudo Acceleration Spectrum in g
% Spv:    Elastic Pseudo Velocity Spectrum in the unit of velocity (e.g. m/s)
% Sd:     Elastic Displacement Spectrum, in the unit of displacement (e.g. m)

function [T,Spa,Spv,Sd]=SPEC(dt,Ag,zet,g,endp)
u=zeros(length(Ag),1);
v=zeros(length(Ag),1);
ac=zeros(length(Ag),1);
Ag(end+1)=0;
T(1,1)=0.00;
for j=1:round(endp/dt)         % equation of motion(Newmark linear method)
    omega(j,1)=2*pi/T(j);      % Natural Frequency
    m=1;       
    k=(omega(j))^2*m;
    c=2*m*omega(j)*zet/100;
    K=k+3*c/dt+6*m/(dt)^2;
    a=6*m/dt+3*c;
    b=3*m+dt*c/2;    
    for i=1:length(u)-1
        u(1,1)=0;                      %initial conditions
        v(1,1)=0;
        ac(1,1)=0;    
        df=-(Ag(i+1)-Ag(i))+a*v(i,1)+b*ac(i,1);  % delta Force
        du=df/K;
        dv=3*du/dt-3*v(i,1)-dt*ac(i,1)/2;
        dac=6*(du-dt*v(i,1))/(dt)^2-3*ac(i,1);
        u(i+1,1)=u(i,1)+du;
        v(i+1,1)=v(i,1)+dv;
        ac(i+1,1)=ac(i,1)+dac;     
    end
    Sd(j,1)=max(abs((u(:,1))));
    %Sv(j,1)=max(abs(v));
    %Sa(j,1)=max(abs(ac))/g;
    Spv(j,1)=Sd(j)*omega(j);
    Spa(j,1)=Sd(j)*(omega(j))^2/g;
    T(j+1,1)=T(j)+dt;
end
Ag(end)=[];
T(end)=[];
Sd(2,1)=0; Spv(1:2,1)=0;Spa(1:2,1)=max(abs(Ag))/g;

%% Plot Spectra
subplot(2,1,1)
%figure('Name','Spectral Displacement','NumberTitle','off')
plot(T,Sd,'LineWidth',2.)
grid on
xlabel('Period (sec)','FontSize',13);
ylabel('Sd (mm)','FontSize',13);
title('Displacement Spectrum','FontSize',13)

subplot(2,1,2)
%figure('Name','Pseudo Acceleration Spectrum','NumberTitle','off')
plot(T,Spa,'LineWidth',2.)
grid on
xlabel('Period (sec)','FontSize',13);
ylabel('Spa (g)','FontSize',13);
title('Pseudo Acceleration Spectrum','FontSize',13)

subplot(2,1,3)
%figure('Name','Pseudo velocity Spectrum','NumberTitle','off')
plot(T,Spv,'LineWidth',2.)
grid on
xlabel('Period (sec)','FontSize',13);
ylabel('Spv (mm/s)','FontSize',13);
title('Pseudo velocity Spectrum','FontSize',13)

%% Use SPEC-Function
clc; 
% clear all; 
close all;
load elcentro.dat   % Load montion, First Col. is the time and the second col. is Acce. in g
g=9810;             % (mm/s^2)
Ag=g*elcentro(:,2); % Acceleration Vector
dt=0.02;            % Time Interval (sec)
zet=2;              % Damping Ratio (%)
endp=5;             % End Period of Spectra (sec) 

%% Recall SPEC.m
[T, Spa, Spv, Sd]=SPEC(dt, Ag, zet, g, endp);

[Jan]

I've formatted the code to improve the readability. Please use the tools on top the section for editing in the future.

Please explain the problem with any details. "Not coming" is too vague to be answered efficiently.

Answer 1

[Bhanu Prakash]

Hi Raj kumar,

As per my understanding, you are trying to perform response spectrum analysis on the function “Elastic spectra” but was not able to plot all the three spectra. In your code you have used “subplot” function with only 2 rows and 1 column, hence it is plotting only two spectra.

To resolve this issue, you can modify the “subplot” function with 3 rows and 1 column to get the third spectra.

To know more about the “subplot” function, please refer to the following link:

Create axes in tiled positions - MATLAB subplot - MathWorks India

I have attached the edited part of the code, for your reference.

%% Plot Spectra 
subplot(3,1,1) 
%figure('Name','Spectral Displacement','NumberTitle','off') 
plot(T,Sd,'LineWidth',2.) 
grid on 
xlabel('Period (sec)','FontSize',13); 
ylabel('Sd (mm)','FontSize',13); 
title('Displacement Spectrum','FontSize',13) 
subplot(3,1,2) 
%figure('Name','Pseudo Acceleration Spectrum','NumberTitle','off') 
plot(T,Spa,'LineWidth',2.) 
grid on 
xlabel('Period (sec)','FontSize',13); 
ylabel('Spa (g)','FontSize',13); 
title('Pseudo Acceleration Spectrum','FontSize',13) 
subplot(3,1,3) 
%figure('Name','Pseudo velocity Spectrum','NumberTitle','off') 
plot(T,Spv,'LineWidth',2.) 
grid on 
xlabel('Period (sec)','FontSize',13); 
ylabel('Spv (mm/s)','FontSize',13); 
title('Pseudo velocity Spectrum','FontSize',13)

Thanks,

Bhanu Prakash.