Spread Footings Research Articles

Mathematical modeling of materially nonlinear problems in structural analyses, Part II: Application in contemporary software

The paper presents application of nonlinear material models in the software package Ansys. The development of the model theory is presented in the paper of the mathematical modeling of material nonlinear problems in structural analysis (part I - theoretical foundations), and here is described incremental-iterative procedure for solving problems of nonlinear material used by this package and an example of modeling of spread footing by using Bilinear-kinematics and Drucker-Prager mode was given. A comparative analysis of the results obtained by these modeling and experimental research of the author was made. Occurrence of the load level that corresponds to plastic deformation was noted, development of deformations with increasing load, as well as the distribution of dilatation in the footing was observed. Comparison of calculated and measured values of reinforcement dilatation shows their very good agreement.

Case studies of three-dimensional effects on the behaviour of test embankments

This paper uses both two-dimensional (2D) and three-dimensional (3D) finite element (FE) analyses to examine three cases involving the construction of full-scale test embankments to failure on soft clay deposits. By comparing the calculated fill thickness at failure from 2D and 3D analyses, it is shown that 3D effects are significant for all test fills, despite the dramatically different locations, fill thicknesses, and underlying clay deposits. In addition, the calculated undrained displacement and extent of failure from 3D analysis agree well with those measured in each case. The risk of neglecting 3D effects is highlighted by the analyses, where it is shown that failure to account for 3D effects while interpreting the response of a test embankment can lead to unsatisfactory performance of the actual long embankment. Finally, by comparing FE analysis results with well-known bearing capacity factors, it is shown that test embankments with a base length to width ratio less than 2 are more strongly influenced by 3D effects than spread footings on similar soil profiles. The analyses presented in this paper provide practical insight into some factors that should be taken into account for the design and construction of embankments and test fills on soft clay deposits.

Experimental and Analytical studies of reinforced crushed limestone

This research study aims at investigating the behavior of spread footings on reinforced crushed limestone using laboratory model tests. The model tests were conducted inside a steel box with dimensions of 1.5 m (length) × 0.91 m (width) × 0.91 m (height) using a steel plate with dimensions of 152 mm × 152 mm (6 in. × 6 in.). The parameters investigated include the number of reinforcement layers and the tensile modulus and type of reinforcement. An analytical solution is also developed to estimate the ultimate bearing capacity of reinforced crushed limestone. The test results show that the inclusion of reinforcement can appreciably improve the bearing capacity of crushed limestone up to a factor of 2.85 at a settlement ratio of 10% and reduce the footing settlement down to 75% at a surface pressure of 5500 kPa. The results also demonstrate that reinforcements with higher tensile modulus performed better than reinforcements with lower tensile modulus and that steel reinforcement performed better than geogrid reinforcement. The proposed analytical solution gave a good predication of experimental results of geogrid reinforced sections, while Huang and Menq's solution (1997) gave a good predication for steel reinforced crushed limestone. The analytical results also showed that the reinforced ratio ( R r) should be high enough to form the “deep footing” effect.

Estimation of bearing capacity for multiple footings in sand

In the present study, the effects of multiple-footing configurations in sand on bearing capacity were investigated using field plate load tests and finite element analyses. Both strip and spread footings were considered in the finite element analyses. In each case, different footing distances were applied for the purposes of comparison among all of the results. From these results, it was observed that the load responses of multiple footings are similar to those of the single footing at distances greater than three times the footing width. Design equation and correlation parameters, necessary for quantifying the values of the bearing capacity ratio for the different multiple-footing configuration, were derived. Experimental test results from the literature were selected and used in verifying the proposed method.

Case Study: Retrofitting Large Bridge Piers on the Nakdong River, South Korea

The Gupo Bridge crosses the Nakdong River near the city of Busan, South Korea. During Typhoon Maemi in 2003, the old Gupo Bridge collapsed due to excessive pier scour. More recently, the highway construction on the left-bank floodplain required right-bank channel widening to restore the channel flood-carrying capacity. This 7 m deep floodplain excavation is expected to cause significant local scour around the 8–10 m wide and 3 m thick spread footings of Piers 11 and 12 of the Subway Bridge and Piers 15 and 16 of the Gupo Bridge. Three design options are examined for retrofitting floodplain bridge piers with massive spread footings. A solution with sheet piles and riprap was recommended in 2006 as the most appropriate design, but Plan III with a conical riprap structure around the footings was ultimately constructed in 2007 for economic reasons. Laboratory experiments also highlight the need to place gravel and synthetic filters under the designed riprap.

Discussion of “Evolution of the Continuous Truss Bridge” by Francis E. Griggs Jr.

As fans of truss bridges in general and of Gustav Lindenthal in particular, we commend the author for his comprehensive review of design, construction, and use of continuous truss bridges in the United States. We are pleased to have the opportunity to add his paper to our library of bridge history and engineering. To supplement the author’s effort, we respectfully offer information on what appears to be a generally overlooked milestone in continuous truss design and construction: the Sellwood Bridge in Portland, Oregon, a four-span continuous truss highway bridge designed by Lindenthal and still in use. Figs. 1 and 2 are recent photos of the bridge. To our knowledge, the four-span continuous figuration is exceedingly rare, if not unique. Also notable is the fact that the Sellwood Bridge opened for traffic in 1925, well before the 1929 Lake Champlain Bridge cited by the author as the first long-span continuous bridge built for highway traffic. Lindenthal himself acknowledged the four-span continuous configuration of the Sellwood truss spans in a 1929 letter to the editor of Engineering News Record as follows: “I believe also that I was the first engineer in this country to use continuous girders on a large scale, in the Sciotoville Bridge. Since then, the Steubenville bridge over the Ohio River, with three spans, was built for the Pennsylvania Railroad; I suggested the continuous system for this bridge and made the check calculations. Only recently I completed two city bridges of the continuous girder type over the Willamette River in Portland, Ore., one of three spans Ross Island Bridge , another of four spans Sellwood . G. Lindenthal, Consulting Engineer, New York City” Lindenthal 1929 The Sellwood Bridge is a two-lane structure over the Willamette River at the south edge of Portland. It now carries about 30,000 vehicles per day, the heaviest-traveled two-lane bridge in Oregon. The approach spans are reinforced concrete, and the main spans are four continuous subdivided Warren-type deck trusses with span lengths of 246, 300, 300, and 246 ft, respectively. Five concrete piers support the truss spans, with one pier founded on timber piles and four on spread footings. As-built drawings indicate that two other piers were designed with piles, but the piles apparently were deleted during construction. The truss spans are supported by a fixed bearing at the center pier and by expansion bearings at the other four piers. Gustav Lindenthal designed the Sellwood Bridge for Multnomah County which includes Portland as part of a multibridge program in the mid-1920s. The county commissioners brought

Spread Footings in Sand: Load Settlement Curve Approach

A study of the assumptions involved in the ultimate bearing capacity equation indicates the shortcomings of that equation and load test data confirm these shortcomings. A new approach using a normalized load settlement curve is proposed to alleviate these shortcomings and to obtain the complete load settlement curve for a footing in sand. The normalization consists of plotting the mean footing pressure divided by a measure of the soil strength within the depth of influence of the footing versus the settlement divided by the footing width. It is shown that the normalized load settlement curve for a footing is independent of footing size and embedment. It is proposed to obtain the normalized curve point-by-point from a soil test. Because the deformation of the soil observed under full-scale footings during loading indicates a barreling effect similar to the soil deformation around a pressuremeter probe, the preboring pressuremeter curve is used to obtain the footing curve. The new method consists of transforming the preboring pressuremeter curve point-by-point into the footing load settlement curve. Load tests and numerical simulations are used to propose a method for a rectangular footing near a slope subjected to an eccentric and inclined load. The new method gives the complete load settlement curve for the footing and alleviates the problems identified with the bearing capacity equation.

Foundations for Integral Abutments

Integral-abutment bridges have many advantages over full-height-abutment or stub-abutment bridges. Integral abutments eliminate or reduce the number of expansion joints in bridge superstructures and simplify design, detailing, and construction. In this paper, foundation design concepts, such as fixed-head pile, pinned-head pile, hinged abutment, fixed-base pile, prebored hole, sleeved pile, and asymmetry are reviewed. The typical foundation type for support of integral abutments is the steel H pile. Depending on bridge length, skew, and site conditions, other types of foundations, such as precast prestressed-concrete pile, pipe pile (steel encased concrete pile or metal shell pile), timber pile, combined H pile (or W section) and drilled shaft, caisson wall, drilled shaft, sheet pile, and spread footing can be used to support integral abutments. Several design methods and proposed limits for typical integral abutment bridges are reviewed.

Design of I-40 Bridges in Guadalupe County, New Mexico

The I-40 in Guadalupe County, New Mexico, contains a set of three bridges. They are medium-span overpasses accommodating two lanes of traffic each. The design team used this routine forum to address several design problems with innovative solutions. In addition, aesthetics were considered from the early stages of design. These two-span bridges are designed continuous for live load by using high-strength prestressed concrete U-beams and cast-in-place deck construction. Three-point bearing provides uniform support of the girders. To alleviate problems with harping and end debonding, strands were added in the top flange, debonded in the center of the beam, and then cut after release. Spread footings on top of backfill of mechanically stabilized earth support the abutments to reduce differential settlement between the approach and the abutment. Differential settlement between pier and abutments was included in the design to account for differences in footing support. The semi-integral abutment stubwall was shortened on each end to allow the integral wingwalls to slide freely; this solved a common movement restraint problem. Aesthetics were considered from the beginning of the project. Three-dimensional modeling was used to visualize the completed form. Artwork was created to form uniform recessions in the concrete. Average bridge costs for these structures, including aesthetics, were below state average. This economy can be attributed to several factors, including simplicity and construction considerations in design, consultation during design with suppliers and contractors, use of repetitive parts and materials, and a creative bid process.

Mechanism of Bearing Capacity of Spread Footings Reinforced with Micropiles

ABSTRACT The Hyogoken-Nambu Earthquake in 1995 caused extensive damages to the foundations of bridges. Ever since, methods to improve the bearing capacity of existing foundations have become an important aspect of foundation engineering in Japan. Micropiles are considered to provide promising solutions. The mechanism which enhances the bearing capacity of surface footings reinforced with micropiles is the subject of investigation in this study. As an initial phase, model tests were conducted to understand the load-displacement behavior of surface footings with and without micropiles on loose, medium dense, and dense layers of sands. Salient factors which influence the behavior of the footings were selected and their influence on bearing capacity was examined through a comprehensive series of model tests. Notable improvements in the bearing capacity of surface footings reinforced with vertical micropile groups were observed in the case of dense sand which is dilative during shear. To assess quantitatively the degree of improvement in the bearing capacity of surface footings reinforced with micropiles, an index R called “Network Effect Index” was introduced in this study. The index R of unity means that the bearing capacity of footings reinforced with micropiles is simply equal to the summation of the individual value of the surface footing and that of the micropile group. An index R of more than two is achieved in this study where surface footings reinforced with a group of vertical micropiles bear on a dense layer of dilative sand. By contrast, with loose and medium dense sand, which are contractive in nature, the index R is found to be less than unity.

Footings under seismic loading: Analysis and design issues with emphasis on bridge foundations

The paper provides state-of-the-art information on the following aspects of seismic analysis and design of spread footings supporting bridge piers: (1) obtaining the dynamic stiffness (“springs” and “dashpots”) of the foundation; (2) computing the kinematic response; (3) determining the conditions under which foundation–soil compliance must be incorporated in dynamic structural analysis; (4) assessing the importance of properly modeling the effect of embedment; (5) elucidating the conditions under which the effect of radiation damping is significant; (6) comparing the relative importance between kinematic and inertial response. The paper compiles an extensive set of graphs and tables for stiffness and damping in all modes of vibration (swaying, rocking, torsion), for a variety of soil conditions and foundation geometries. Simplified expressions for computing kinematic response (both in translation and rotation) are provided. Special issues such as presence of rock at shallow depths, the contribution of foundation sidewalls, soil inhomogeneity and inelasticity, are also discussed. The paper concludes with parametric studies on the seismic response of bridge bents on embedded footings in layered soil. Results are presented (in frequency and time domains) for accelerations and displacements of bridge and footing, while potential errors from some frequently employed simplifications are illustrated.

アウグスタの飛行船格納庫の劣化現況調査(材料施工)

This paper presents the results of deterioration investigation of the ancient airship military Hangar in Augusta, Italy, which construction began in 1917. The stability of the airship hangar is now threatened by the differential settlements of its spread footings and a research project is currently underway to strengthen the hangar. In this paper, 1) deterioration of the wall and roof, 2) bar arrangement and its corrosion, 3) depth of neutralization and included chloride ion, 4) fundamental frequency, and 5) monitoring of temperature, inclination of buttress pier, width of the significant cracks and extension of the wire are discussed.

Effect of Spread Footing Flexibility on Structural Response

Spread footings are normally used under individual columns of buildings and bridge piers. They are economical to use and are applicable for any soil conditions where the bearing capacity for the applied loads is adequate. Structural design codes and specifications allow a linear soil pressure distribution to be assumed for the design of spread footings. This approach is valid for infinitely rigid footings. Past experience has shown that the assumption of a linear pressure distribution is satisfactory for most footings; however, there are some cases in which a shallow foundation must be analyzed as a flexible structure, particularly if the footing is excessively long/wide and thin. In this study, a relative stiffness factor, Kr′ , is developed that can determine whether a footing can be considered rigid for the purposes of structural analysis and design. This factor is a modified version of an expression first proposed by Meyerhof in 1953, but takes into account the size of the column supported on the foot...

ROCKING ISOLATION OF A TYPICAL BRIDGE PIER ON SPREAD FOUNDATION

It has been observed that after some earthquakes a number of structures resting on spread footings responded to seismic excitation by rocking on their foundation and in some cases this enabled them to avoid failure. Through application to a standard bridge supported by direct foundations, this paper discusses the major differences in response when foundation uplift is taken into consideration. Special focus is given on the modifications of rocking response under biaxial and triaxial excitation with respect to uniaxial excitation. It is found that inelastic rocking has a significant isolation effect. It is also shown that this effect increases under biaxial excitation while it is less sensitive to the vertical component of the earthquake. Finally, parametric analyses show that the isolation effect of foundation rocking increases as the size of the footing and the yield strength of the underlying soil decreases.

Design of Short Aggregate Piers to Support Highway Embankments

When new embankments are constructed over soft soils and existing roadways and embankments are widened rapidly, stability and differential settlement problems often result. Past approaches to mitigate these problems include overexcavation and replacement, preloading, lightweight fill, piles and concrete caps, geosynthetic-reinforced soil and pile-supported embankment systems, stone columns, lime-cement columns, and deep soil mixing. The advantages and limitations of these approaches are well documented in the literature. An alternative approach to support highway embankments that is less well documented, but that has seen increased use in recent years, is short aggregate piers. Although the technique has been used to support shallow spread footings, design approaches and parameter values have not been widely available for embankment support applications and are not well known in the field. The engineering properties and an approach used to design short aggregate piers for the support of highway embankments are summarized, and the mechanisms of load-settlement behavior are described. Techniques for evaluating overall stability, control and time rate of settlement, and bearing capacity are summarized. Performance measurements are referenced for embankment support projects recently constructed in Iowa.

Evaluation of Cone Penetration Test-Based Settlement Prediction Methods for Shallow Foundations on Cohesionless Soils at Highway Bridge Construction Sites

The cone penetration test (CPT) method is gaining popularity in the United States as one of the premier subsurface exploration techniques. The writers previously monitored settlement behavior of spread footing foundations at five highway bridge construction sites in Ohio and evaluated the standard penetration test-based settlement prediction methods in light of the field performance data. The authors recently conducted CPT sounding at these bridge sites. In this paper, settlement behavior of five spread footings resting on cohesionless soils at two sites were predicted with the CPT-based settlement prediction methods proposed by Amar, DeBeer, Meyerhof, and Schmertmann. The results showed that the prediction methods by Schmertmann and DeBeer were both conservative but reasonably reliable in predicting the settlement of shallow foundations observed in the field.

Pyrite oxidation in Lower Lias Clay at concrete highway structures affected by thaumasite, Gloucestershire, UK

The process of pyrite oxidation with the resulting formation of sulfates in disturbed pyrite-rich mudstone is recognised in the UK as a potential engineering hazard. This paper describes and quantifies the extent of pyrite oxidation in Lower Lias Clay in Gloucestershire using a large data set collected in 1998 and 1999 during the investigation of twenty-eight, approximately 30-year old highway structures affected by the thaumasite form of sulfate attack. Most of the structures have concrete spread footings founded on undisturbed and relatively unweathered Lower Lias Clay, and are surrounded by backfill of reworked Lower Lias Clay. Chemical, X-ray diffraction and X-ray fluorescence analyses are used to determine the composition of the soils. Differences are identified in the sulfides, sulfates and total sulfur concentrations between unweathered and weathered Lower Lias Clay and the backfill. The work is supported by pyrite oxidation trials in the laboratory on clay samples stored in bags and sealed tubes. The results indicate that pyrite oxidation, sulfate formation and leaching have occurred as the Lower Lias Clay weathers in situ and also during and following disturbance and reworking for highway construction. The amount and rate of pyrite oxidation are estimated, and comparison is made with the concentration of sulfate in the surrounding groundwater, and the extent of thaumasite sulfate attack measured at adjacent structures.

Shrink Test–Water Content Method for Shrink and Swell Predictions

A new method is proposed to estimate the vertical movement of the ground surface for soil that swells and shrinks due to variations in water content. The water content is used as the main soil parameter and a shrink test is suggested to obtain the relationship between the change in water content and the volumetric strain induced. We propose estimating the change in water content and the depth of seasonal moisture changes from local databases or from existing techniques. The method is evaluated by comparing the predicted movement and the measured movement of four full-scale spread footings over a period of 2 years.

A Simplified Computation of the Interactive Behavior between Soils and Framed Structures

In common structural design practice, the foundation loads from structure analysis are obtained without allowance for soil settlements, and the foundation settlements are estimated under the assumption of a perfectly flexible structure. However, the stiffness of the structure influences the distribution of the load transferred to the foundation; and hence the settlements, and soil settlements affect the load distribution on the foundation and the stresses set up in the structure. This paper presents an efficient and simple procedure for the analysis of the interaction behavior of two-dimensional framed structures supported by spread footings founded on different soil profiles. The interactive behavior between soils and a variety of two-dimensional multi-bay framed structures was evaluated. Interaction between soil and structure has been found to significantly affect the estimated settlements, footing loads, and internal forces in the superstructure members. The footing loads were found to increase or decrease due to the consideration of the effect of soil-structure interaction. This comparably influenced the internal forces and stresses within the structure members.

Probabilistic Foundation Settlement on Spatially Random Soil

By modeling soils as spatially random media, estimates of the reliability of foundations against serviceability limit state failure, in the form of excessive differential settlements, can be made. The soil's property of primary interest is its elastic modulus, E, which is represented here using a lognormal distribution and an isotropic correlation structure. Prediction of settlement below a foundation is then obtained using the finite element method. By generating and analyzing multiple realizations, the statistics and density functions of total and differential settlements are estimated. In this paper probabilistic measures of total settlement under a single spread footing and of differential settlement under a pair of spread footings using a two-dimensional model combined with Monte Carlo simulations are presented. For the cases considered, total settlement is found to be represented well by a lognormal distribution. Probabilities associated with differential settlement are conservatively estimated through the use of a normal distribution with parameters derived from the statistics of local averages of the elastic modulus field under each footing.