Cheng Lan

Application of Topological Optimization to Bridge Design

AbstractRecently, structural optimization has become an important tool for structural designers, because it allows a better exploitation of material, thus decreasing a structure’s self-weight and saving material costs. Moreover, structural optimization helps the designer to find innovative design solutions and structural forms that not only better exploit material but also give the structure greater aesthetic value from an architectural point of view. In this article, the seismic retrofitting of a bridge originally designed in reinforced concrete is illustrated, showing how lightening the bridge superstructure, rather than reinforcing the already completed foundations and abutments, allowed these latter features to resist greater seismic actions as required in the recent update of the Italian seismic code. Therefore, besides using the steel-concrete composite typology, the bridge superstructure was lightened through structural optimization. After having optimized the thickness of webs and flanges, it was ...

Optimization Indexes to Identify the Optimal Design Solution of Shell-Supported Bridges

As a structural optimization technique, topology optimization is an important tool for helping designers to determine the most suitable shape of a structure. With this powerful tool, designers can define families of candidate solutions by modifying the input volume reduction (VR) ratio, reducing the structural weight as much as possible. However, finding the best compromise between material savings and structural performance among these candidate solutions is a critical issue for designers. To deal with this issue, an optimization index (OI) is presented in this paper. It provides a mathematical procedure that highlights the best choice among several candidate solutions obtained by the optimization procedure. The index was originally defined in a previous study on the structural optimization of composite steel-concrete bridges. In this paper, a generalized version of the original optimization index is introduced and used to investigate a particular aspect related to concrete shell-supported bridges. Starting from three shell-supported footbridges, the shapes of which are the final result of form-finding optimization procedures, different starting models are defined, and each is characterized by different edge-stiffening conditions. Despite using an anticlastic shell shape, unavoidable tensile stresses occur because of the thickness of the shell, variations in the material, the loading of the deck, and other factors. For each starting model, a finite-element topological optimization conducted with the solid isotropic material with penalization (SIMP) method is performed to minimize the weight (i.e., volume) of the shell by a certain percentage. According to the results obtained from topology optimization, the proposed generalized optimization index (OI*) analytical formulation is discussed in detail, and its effectiveness is validated.

Application of digital photogrammetry in wind tunnel test for bridge model

Abstract Wind tunnel test of aeroelastic model is the principal means to research the performance of bridge structures in wind flow. Laser interferometer and accelerometer are the two mainly used instruments to measure the wind-induced response of models in wind tunnel test. However, due to limitation of some cases, these two instruments are inapplicable or at least unreliable. Digital image recognition photogrammetry is the technique combining photogrammetry and image recognition. Based on digital photogrammetry (DP), movement information of measured object is recorded by digital video equipment as a series of continuous frames and its accurate position in world coordinate can be recognised by analysis arithmetic. Wind tunnel tests of two bridges were introduced in this paper to verify the applicability of two DP methods, geometry analysis and area-centroid. The analysis result showed that DP provided the signal of high quality and proved a reliable means to compensate the traditional methods for wind tunnel test.