Ctrl+K

Influence line shear force

Influence line shear force#

Click –> Live Code on the top right corner of this screen to investigate some influence lines!

figuur 1

import micropip
await micropip.install("ipympl")

import numpy as np
import sympy as sym
import matplotlib.pylab as plt
from ipywidgets import widgets, interact
from matplotlib.patches import Arc,StepPatch

%matplotlib widget

EI, x = sym.symbols('EI, x',real=True)

Av, Am = sym.symbols('Av, Bv',real=True)
a, L= sym.symbols('a, L ',positive=True,real=True)
C1, C2, C3, C4 = sym.symbols('C1, C2, C3, C4')

q = -Am * sym.SingularityFunction(x,0,-2) - Av * sym.SingularityFunction(x,0,-1) + 1 * sym.SingularityFunction(x,a,-1)
V = -sym.integrate(q,x)+C1
M = sym.integrate(V,x)+C2
kappa = M / EI
phi = sym.integrate(kappa,x)+C3
w = - sym.integrate(phi,x)+C4
eq1 = sym.Eq(w.subs(x,0),0)
eq2 = sym.Eq(phi.subs(x,0),0)
eq3 = sym.Eq(M.subs(x,-1),0)
eq4 = sym.Eq(M.subs(x,L),0)
eq5 = sym.Eq(V.subs(x,-1),0)
eq6 = sym.Eq(V.subs(x,L+1),0)
sol = sym.solve([eq1,eq2,eq3,eq4,eq5,eq6],[C1,C2,C3,C4,Av,Am])
V_sol = V.subs(sol)
V_subs = V_sol.subs([(L,6),(a,2),(EI,5000)])
V_numpy = sym.lambdify([L,a,EI,x],V_sol.rewrite(sym.Piecewise))
M_sol = M.subs(sol)
M_subs = M_sol.subs([(L,6),(a,2),(EI,5000)])
M_numpy = sym.lambdify([L,a,EI,x],M_sol.rewrite(sym.Piecewise))

Find V-line#

def vervormingV(locationx,locationy,scale,flip=0,rotation=0):
    axs = plt.gca()
    vx = [-0.5,0,0,0.5]
    if flip==0:
        vy = [0.25,0.25,-0.25,-0.25]
    elif flip==1:
        vy = [-0.25,-0.25,0.25,0.25]
    vxr= np.add(np.multiply(np.cos(rotation/180*np.pi),vx),np.multiply(np.sin(rotation/180*np.pi),vy))
    vyr= np.add(np.multiply(np.sin(rotation/180*np.pi),vx),-np.multiply(np.cos(rotation/180*np.pi),vy))
    vxscaled = np.add(locationx,np.multiply(scale,vxr))
    vyscaled = np.add(locationy,np.multiply(scale,vyr))
    axs.plot(vxscaled,vyscaled,color='black',linewidth=1)
    axs.axis('equal')

display(sym.simplify(V_subs.rewrite(sym.Piecewise)))

plt.figure()
x_plot = np.linspace(0,5.00001,1000)
x_plot = np.linspace(-0.0001,6,1000)
plt.plot([0,6],[0,0],color='black',linewidth=2)
plt.plot(x_plot,V_numpy(L=6,a=2,EI=1500,x=x_plot),color="blue")
plt.xlabel('$x$')
plt.ylabel('Shear force')
axs = plt.gca()
axs.grid()
axs.invert_yaxis()
title0 = 'Shear force distribution for force at $x_F =  2 $'
vervormingV(1,0.3,0.3,0)
axs.set_title(title0);
axs.spines['right'].set_color('none')
axs.spines['top'].set_color('none')
axs.spines['bottom'].set_position('zero')
axs.spines['left'].set_position('zero')
plt.show()
\[\begin{split}\displaystyle \begin{cases} 0 & \text{for}\: x > 2 \\-\infty & \text{for}\: x = 0 \\1 & \text{for}\: x > 0 \\0 & \text{otherwise} \end{cases}\end{split}\]

Find influence line V#

q = -Am * sym.SingularityFunction(x,0,-2) - Av * sym.SingularityFunction(x,0,-1) 
V = -sym.integrate(q,x)+C1
M = sym.integrate(V,x)+C2
kappa = M / EI
phi = sym.integrate(kappa,x)+C3 
w = -sym.integrate(phi,x)+C4 + sym.SingularityFunction(x,a,0)
eq1 = sym.Eq(w.subs(x,0),0)
eq2 = sym.Eq(phi.subs(x,0),0)
eq3 = sym.Eq(M.subs(x,-1),0)
eq4 = sym.Eq(M.subs(x,L),0)
eq5 = sym.Eq(V.subs(x,-1),0)
eq6 = sym.Eq(V.subs(x,L+1),0)
sol = sym.solve([eq1,eq2,eq3,eq4,eq5,eq6],[C1,C2,C3,C4,Av,Am])
w_sol = w.subs(sol)
w_subs = w_sol.subs([(L,6),(a,2),(EI,1500)])
#display(sym.simplify(w_subs.rewrite(sym.Piecewise)))
V_inf_numpy = sym.lambdify([L,a,EI,x],w_sol.rewrite(sym.Piecewise))

plt.figure()
x_plot = np.linspace(0,6,1000)
plt.plot([0,6],[0,0],color='black',linewidth=2)
plt.plot(x_plot,V_inf_numpy(L=6,a=2,EI=1500,x=x_plot),color="blue")
plt.xlabel('$x_F$')
plt.ylabel('Influence factor shear force')
axs = plt.gca()
axs.grid()
axs.invert_yaxis()
title0 = 'Influence line for shear force at $x_V = 2$'
axs.set_title(title0);
axs.spines['right'].set_color('none')
axs.spines['top'].set_color('none')
axs.spines['bottom'].set_position('zero')
axs.spines['left'].set_position('zero')
plt.show()

Comparison V-line and influence line for shear force at \(x = ...\)#

fig, axs = plt.subplots(2, 1, figsize=(7, 6))
x = np.linspace(0,5.0001,200)
def func(a,b):
    axs[0].clear()  # Clear the existing plot
    axs[1].clear()
    axs[0].plot([0,6],[0,0],color='black',linewidth=2)
    axs[0].grid()
    axs[0].axis('equal')
    axs[0].plot(x,V_numpy(6,b,1500,x),color='blue')
    axs[0].plot(a,V_numpy(6,b,1500,a),marker='o')
    axs[0].annotate('%.2f kN' % V_numpy(6,b,1500,a),xy = [a,V_numpy(6,b,1500,a)+0.2])
    axs[0].annotate(text='', xy=(b,0), xytext=(b,-0.3), arrowprops=dict(arrowstyle='simple'))
    axs[0].invert_yaxis()
    plt.sca(axs[0])
    vervormingV(b/2,V_numpy(6,b,1500,x)[1]/2,V_numpy(6,b,1500,x)[1]/2,0)
    title0 = 'Shear force distribution for force at $x_F = '+str(b)+'$, showing shear force at $x_V = '+str(a)+'$'
    axs[0].set_title(title0)
    axs[1].plot([0,6],[0,0],color='black',linewidth=2)
    axs[1].grid()
    axs[1].axis('equal')
    axs[1].plot(x,V_inf_numpy(6,a,1500,x),color='blue')
    axs[1].plot(b,V_inf_numpy(6,a,1500,b),marker='o')
    axs[1].annotate('%.2f kN' % V_inf_numpy(6,a,1500,b),xy = [b,V_inf_numpy(6,a,1500,b)+0.2])
    axs[1].invert_yaxis()
    title1 = 'Influence line for shear force at $x_V = '+str(a)+'$'
    axs[1].set_title(title1)

    axs[0].spines['right'].set_color('none')
    axs[0].spines['top'].set_color('none')
    axs[0].spines['bottom'].set_position('zero')
    axs[0].spines['left'].set_position('zero')
    axs[1].spines['right'].set_color('none')
    axs[1].spines['top'].set_color('none')
    axs[1].spines['bottom'].set_position('zero')
    axs[1].spines['left'].set_position('zero')
    plt.draw()  
    
interact(func, a = widgets.FloatSlider(min=0, max=6, value=2, step=0.1, description="Location shear force x_V = ... (m)",readout_format='.1f',style= {'description_width': '200px'},layout = {'width': '450px'}),
         b = widgets.FloatSlider(min=0, max=6, value=2, step=0.1, description="Location force x_F = ... (m)",readout_format='.1f',style= {'description_width': '200px'},layout = {'width': '450px'}) );
Contents