This article first proposed a Bipartite Request Dependency Graph (BRDG) that describes the object-level interrelationships between user click requests and embedded web object requests. These two kinds of requests are classified from HTTP data by an identification algorithm. The interrelationships between user click requests and embedded web object reflect the web page structural, which contain latent web information. Exploring structural patterns is crucial for many aspects like web security analysis and web information visualization. Accordingly, the article also proposed a novel graph decomposition method called orthogonal nonnegative matrix tri-factorization (tNMF) to the BRDG. Compared to traditional web graph analysis focus on statistical and structural properties of the whole graph, the proposed method is dedicated to mine latent web structural patterns. Decomposition results demonstrate that several interesting structures exist in the BRDG. The article aims at classifying these subgraphs as several structural patterns and shedding light on the causes of these patterns.