Structural Health Monitoring in Incrementally Launched Steel Bridges: Patch Loading Phenomena Modeling

Highlights

• A realistic 3D nonlinear simulation of bridge launching is presented.

• Results concerning stress, strain and displacement fields are depicted.

• The model provides information that may be used during construction.

• Results are used for inferring patch loading failure during launching.

• A proposal for defining failure and malfunctioning limits is included.

Abstract

In this paper, a realistic nonlinear 3D simulation of an incrementally launched steel bridge girder is presented. The numerical simulation accounts for three sources of nonlinearity: geometry, material and boundary conditions. For the sake of depicting the capabilities of the presented numerical model in structural verifications, the study is focused on the patch loading field, a structurally complex phenomenon. Patch loading (or concentrated loading) is one of the most typically encountered structural verifications on incrementally launched steel I-girders. The presented realistic simulation is based upon an experimentally calibrated numerical model and may provide relevant information at both design and construction stages. For the former, the predictive capabilities of the model for inferring the potential failure due to patch loading are depicted. For the latter, the results obtained are displayed in a way that may be useful for planning a Structural Health Monitoring (SHM) deployment aimed at controlling the patch loading-related phenomena in incrementally launched steel plate girders.

Introduction

The incremental launching method (ILM) consists of a construction process for bridges in which the superstructure is assembled on one side of the obstacle to be crossed and then pushed longitudinally into its final position. The launching is typically performed statically in a series of increments from one side to another. The (ILM) for bridge construction was first used in Venezuela in a bridge over the Caroni River as described in [1]. Ever since that, the method has evolved technically, economically and in practicality with better launching devices, better control of the pushing systems, better accuracy in topographic field measurements and better understanding of the structural phenomena involved. As a result, it is estimated that thousands of concrete and/or steel bridges have been incrementally launched worldwide [2]. An extensive review of practical applications of the method can be found in [3], [4], [5], [6], [7]. The ILM has gained popularity in recent decades among owners and contractors since it may often be the most reasonable way to construct a bridge over an inaccessible or environmentally protected obstacle. The method may guarantee minimal disturbances to the surroundings which may be of a great concern during construction. The ILM, however, may not be the most economical procedure for constructing all bridges. First, at design stages, a thorough structural analysis of a considerable amount of steps is required. The process involves a continuous change of the structural schemes of the bridge with varying geometries, loads and boundary conditions. Second, at construction stages, a considerably specialized construction equipment and expertise are needed. All the potential advantages the ILM may offer when compared to other methods presume that both careful design as well as execution control are provided. The literature describing successful construction procedures using ILM worldwide is vast [8], [9], [10], [11], [12]. Third, it is also pinpointed though that works reporting incidents during the ILM process are not infrequent [13], [14], [15], [16].

Fig. 1 depicts a 3D view of a hypothetically launched steel girder. Both transversally stiffened and unstiffened cross-sections pass over the supporting bearings. For relatively long girders, the vertical reaction of the bearing induced by the self-weight may be considerably high and potentially harmful for the web when acting over an unstiffened cross-section. As steel girders are typically slender, these reactions may induce an instability-related failure on the web. A concentrate load acting over an unstiffened web of a cross-section is commonly referred to as patch loading. The geometry of the girder (thicknesses t_w and t_f, height h_w, flange width b_f, distance between transverse stiffeners a and bearing length s_s) as well as the web material properties f_yw are determinant parameters on the resistance of steel girders subjected to concentrated loading.

Furthermore, in recent years, Structural Health Monitoring (SHM) has evolved in a considerably fast fashion. Data acquisition and power supply are increasingly more robust [17], [18]. Likewise, wireless technologies provide feasible means of data gathering during both the life span and/or the whole construction procedures in bridges [19], [20], [21]. In last decades, the SHM deployments on incrementally launched bridges have been focused on gathering displacement data as well as reaction forces via load cells or launching devices. Research and field engineering works related to SHM in incrementally launched steel bridges have been reported in recent years in the literature [22], [23], [24], [25], [26].

The advent of wireless technologies in SHM opens a considerable amount of possibilities for short- and long-term bridge monitoring [27]. Particularly, in the near future, the whole construction process of incrementally launched steel bridges may considerably be monitored with power-autonomous, wirelessly connected sensors that would eventually provide a vast amount of information to practice engineers. Subsequently, the feasibility of data-gathering diverts the technical difficulties to the need of storing, processing, understanding and visualizing this data deluge. Considerable attention is nowadays paid to data management in SHM in different civil engineering fields, especially for long-term monitoring deployments as shown in [28], [29], [30], [31]. SHM deployments should provide sufficient but manageable information to structural engineers. A good balance between both quantity and quality of data requires bespoken deployments for each construction procedure. In each case, a thorough understanding of the most critical structural phenomena involved is compulsory.

In this paper, an experimentally calibrated realistic 3D numerical simulation accounting for geometrical, material and boundary conditions nonlinearity is presented. This numerical modeling provides information that may be used for understanding the patch loading structural phenomenon and thus, for conceiving a meaningful deployment for SHM of incrementally launched steel I-girders aimed at monitoring this potential failure mode during construction. The main objective of the paper is to show to practice engineers, which type of information may be useful when deciding both the type and the amount of necessary monitoring technologies. The numerical simulation is systematically exploited with patch loading, but it may also be extended to other typical verifications such as lateral torsional buckling or shear buckling, which also represent quite frequent structural verifications that have also been considerably studied theoretically, experimentally and numerically.