Inspection and Process of Tension of Cables of General Rafael Urdaneta Bridge

In 1997 and 1999, inspection works were carried out in the 384 cable stays of the six central piers of General Rafael Urdaneta Bridge, located in Maracaibo, Venezuela. Inspection indicated the presence of water and significant settlings in the sockets of the cables and corrosion along each cable and socket. The tension of the cables was also measured, and differences of up to 30% in the tension of the cables of some of the 24 groups corresponding to the six central piers (four groups of 16 for each pier) were found. The results suggested the need to retension the cables. This paper shows the outcome of the inspection and indicates the procedure and results of the process of retension, finished in July 2000.     

Maximum Local Scour Depth at Bridge Piers under Unsteady Flow

The temporal effect of hydrograph on local scour depth is investigated under clear-water scour condition. By analyzing the characteristics of scour-depth evolutions at bridge piers for different rising hydrographs, a relation for estimating the maximum scour depth in uniform sediment is proposed. In the relation, the flow unsteadiness effect is taken into account by an unsteady flow parameter combining the peak-flow intensity and time-to-peak factors. For nonuniform sediment with d84 employed as the effective sediment size, this relation can yield reasonably good results of the maximum scour depth under rising hydrograph.     

A Robust Macroelement Model for Soil–Pile Interaction under Cyclic Loads

The principal focus of this study is the development of a robust macroelement model for soil–pile interaction under cyclic loads. The model incorporates frictional forces and formation of gaps at the soil–pile interface as well as hysteretic behavior of the soil. The plastic envelope of the soil behavior is modeled via the so-called p–y approach, outlined in American Petroleum Institute’s guidelines for design of foundation piles for offshore platforms. The macroelement is an intuitive assembly of various basic elements, each of which incorporating a particular aspect of the soil–pile interaction. The modular structure of this macroelement allows straightforward adaptation of improved constitutive models for its building blocks. Herein, we focus on large-diameter, cast-in-drilled-hole reinforced concrete piles (piers) that are partially or fully embedded in soil. These types of piles are frequently used as support structures in highway construction. Consequently, the numerical robustness of the interaction model is assessed with parametric studies on pile systems and soil types relevant to this type of construction. Both elastic and inelastic pile behaviors are considered in the parametric studies. The results indicate that the proposed interaction element is numerically robust, and thus, amenable to routine structural analysis.     

Coupled Macroelement Model of Soil-Structure Interaction in Deep Foundations

The principal objective of this study is the development and calibration of a macroelement model for soil-pile interaction under simultaneously applied lateral and vertical loads. Herein, we focus on cast-in-drilled-hole single piles that are partially or fully embedded in soil, which are frequently used as support structures in highway construction. The model is calibrated and verified using primarily three-dimensional finite-element simulations and, whenever possible, with experimental data obtained from open literature. These data indicate that lateral loads significantly affect the vertical response of single piles, whereas the converse coupling is negligible. The proposed macroelement model is capable of mimicking this phenomenon. As such, it is a computationally efficient alternative to finite-element analyses, and is feasible to be utilized in practical applications.     

Influence of Wood Debris Accumulation on Bridge Pier Scour

This note deals with the influence of debris accumulation on scour around bridge piers. Clear-water experiments in different hydraulic conditions have been carried out with three wood debris shapes: rectangular, triangular, and cylindrical. A wide range of debris thickness and width were studied in order to determine their influence on the maximum scour hole depth temporal evolution. The ratio of the pier diameter to the channel width was varied between 0.05 and 0.12 with total bridge contractions up to 20%. A proposed relation presents a simple design procedure to predict the increase in scour depth, which mainly depends on the flow contraction due to the debris accumulation.     

Experimental Investigation of Grouted Helical Piers for Use in Foundation Rehabilitation

Building rehabilitation is critical for numerous older urban areas, many of which have inadequate foundations to support new demands. Consequently, development of practical methods to strengthen existing foundations is crucial. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues by strengthening the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then helical piers provide the ability to deliver grout. It is hypothesized that these grouted helical pier systems could address foundation strengthening needs. This paper presents findings from an exploratory research program where grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at the University of California, Davis. Experimental methods and procedures developed are presented, and observations regarding the formation of grout bulbs under different conditions are analyzed. Physical observation of the test specimens indicates that average grout bulb diameters of 0.6–1.9 times the helix diameter (Dh) are attainable. For similar grout mixes, 20–50% larger grout bulbs can be attained by adding just a modest amount of injection pressure. Future research may use these results to develop load performance data.     

Clearwater Local Scour at Complex Piers

A new methodology to predict local scour depth at a complex pier is presented herein that combines existing expressions for scouring respectively at uniform piers, caisson-founded piers, pile groups with debris rafts, and pile groups alone. The method recognises the relative scouring potentials of the components of complex piers and the transition of scouring processes occurring for varying pile-cap elevation. The validity of the method is confirmed herein using the present and also historical measurements of local scour at complex piers. The proposed methodology has the advantages of being conceptually consistent with observed scour behaviours, relatively simple to apply, applicable to wide ranges of flow and sediment conditions (through incorporation into a more general analysis framework), and applicable over the entire range of possible pile-cap elevations. For design purposes, the present method highlights respective pile-cap elevations that maximize (i.e., to be avoided over the pier life) and minimize local scour at complex piers. The present method reinforces that where the pile-cap elevation relative to the bed can vary with time at a bridge site, potential local-scour depths need to be assessed over the range of possible pile-cap elevations for the pier.     

Stress Zones near Displacement Piers: II. Radial Cracking and Wedging

Transient liquefaction of saturated soils near Rammed Aggregate Piers is described in Part I on the basis of radial stress measurements. This is supported by dynamic pore-water pressure measurements, as peak pore pressures approximately equal radial stresses imposed at the pier surface by ramming. Stress measurements outside of the liquefied/plastic zone indicate radial tension cracking in the elastic zone, which is consistent with the observation that pore pressures abruptly drop and momentarily can even become negative as soon as ramming stops. The drainage field created by extended radial cracking and hydraulic fracturing allows Rammed Aggregate Piers to be effective in saturated, fine-grained soils where other dynamic methods are reported to be less effective. Stress measurements indicate that liquefied soil injected into open tension cracks causes stress to be retained in the elastic zone through arching action. A stress path analysis indicates that lateral stress may play an important role in control of foundation settlement, by simulating an increase in the preconsolidation pressure without vertically surcharging the soil or waiting for it to consolidate.     

用ANSYS对连续刚构桥进行优化研究

深入研究了 ANSYS 软件的优化功能模块,并以某大跨连续刚构桥为研究对象,提出了通过分节段优化进而达到全桥沿纵向优化的思路。在保证刚度和强度的条件下,通过对双肢薄壁墩壁厚的优化,使桥梁总重量减少了5.7%;通过对箱梁各部分厚度的优化,使得桥梁的总重量减少了2.5%。说明桥梁设计时优选腹板顶、底板的合理比例是必要的,适当减小双薄壁墩的壁厚是切实可行的,可提高结构性能,减少工程造价。     

Experimental Study of Three-Dimensional Flow Field around a Complex Bridge Pier

In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching boundary layer at the upstream of the pile cap separated in two vertical directions and induced an upward flow toward the column and a contracted downward flow below the pile cap and toward the piles. The contracted upward flow on the pile cap interacts with downflow in the front of the column and deflects toward the side of the pier, which in return produces a strong downflow along the side of the pile cap. The flow at the rear of the pile cap is very complex. The strong downward flow at the downstream and near the top of the pile cap in interaction with the reverse flow behind the column and upward flow near the bed produce two vortices close to the upper and lower corners of the pile cap with opposite direction of rotation. On the other hand, the back-flow from the wake of the pile cap is forced into the top region resulting in a secondary recirculation at the wake of the column. The contracted flow below the pile cap and toward the piles, a strong downflow along the sides of the pile cap at the upstream region, and a vortex flow behind the pile cap and an amplification of turbulence intensity along the sides of the pile cap at the downstream region are the main features of the flow responsible for the entrainment of bed sediments.