Summary: We study the multiplicity of nontrivial solutions for nonlinear wave equations of the form \(u_{tt}-u_{xx}=b[(u+1)^+-1]\) in \((c,d)\times \mathbb{R}\) with Dirichlet boundary condition on the interval \(c<x<d\). We find the multiple nontrivial solutions of the equation. Here we reduce this problem into a two-dimensional problem by using variational reduction method and apply the mountain pass theorem to find the nontrivial solutions.