Sivapalan Gajan

Application and Validation of Practical Tools for Nonlinear Soil-Foundation Interaction Analysis

Practical guidelines for characterization of soil-structure interaction (SSI) effects for shallow foundations are typically based on representing foundation-soil interaction in terms of viscoelastic impedance functions that describe stiffness and damping characteristics. Relatively advanced tools can describe nonlinear soil-foundation behavior, including temporary gap formation, foundation settlement and sliding, and hysteretic energy dissipation. We review two tools that describe such effects for shallow foundations and that are implemented in the computational platform OpenSees: a beam-on-nonlinear-Winkler foundation (BNWF) model and a contact interface model (CIM). We review input parameters and recommend parameter selection protocols. Model performance with the recommended protocols is evaluated through model-to-model comparisons for a hypothetical shear wall building resting on clay and model-data comparisons for several centrifuge test specimens on sand. The models describe generally consistent moment-rotation behavior, although shear-sliding and settlement behaviors deviate depending on the degree of foundation uplift. Pronounced uplift couples the moment and shear responses, often resulting in significant shear sliding and settlements. Such effects can be mitigated through the lateral connection of foundation elements with tie beams.

Effects of Moment-to-Shear Ratio on Combined Cyclic Load-Displacement Behavior of Shallow Foundations from Centrifuge Experiments

Current design guidelines for shallow foundations supporting building and bridge structures discourage footing rocking or sliding during seismic loading. Recent research indicates that footing rocking has the potential to reduce ductility demands on structures by dissipating earthquake energy at the footing-soil interface. Concerns over cyclic and permanent displacements of the foundation during rocking and sliding along with the dependence of foundation capacity on uncertain soil properties hinder the use of footing rocking in practice. This paper presents the findings of a series of centrifuge experiments conducted on shear wall-footing structures supported by dry dense to medium dense sand foundations that are subjected to lateral cyclic loading. Two key parameters, static vertical factor of safety ( FSV ) , and the applied normalized moment-to-shear ratio (M∕ (H⋅L) ) at the footing-soil interface, along with other parameters, were varied systematically and the effects of these parameters on footing-so...

Settlement Rehabilitation of a 35-Year-Old Building: Case Study Integrated with Analysis and Implementation

This paper presents a rehabilitation project concerning the settlement of a 35-year-old building. The foundation system of the northwest wing of the building consists of strip footings and slab on grade. Differential settlement results in significant cracking of the masonry partition walls located on the footing, and hence rehabilitation of the footing is required to stabilize the foundation system. Geotechnical and structural investigations are conducted, including site borings and analytical modeling on the basis of one-dimensional consolidation theory that is incorporated into a finite-element analysis. The predictive model exhibits that the differential settlement does not cause noticeable distress for the primary structural members, whereas the continued settlement affects use of the building. Site implementation is performed with the push-pile method to terminate the continuous settlement of the foundation.

Application of probabilistic methods to characterize soil variability and their effects on bearing capacity and settlement of shallow foundations: state of the art

Abstract This paper presents the applications of probabilistic methods to analyze the load-displacement behavior of shallow foundations supported by uncertain and spatially variable soils. The paper describes the types and sources of uncertainties in soil properties that dictate the bearing capacity and settlement of shallow foundations and characterizes their probabilistic distributions. General probabilistic analysis methods that are commonly used in foundation engineering applications such as first order second moment (FOSM) method, tornado diagram method, Monte Carlo (MC) simulation method, random finite element method (RFEM), and reliability-based design (RBD) method are briefly described. A thorough summary of the applications of these methods in determining the probabilistic bearing capacity, settlement, and differential settlement of shallow foundations from the research literature is presented.

Improved Design of Embedment Depths for Transmission Pole Foundations Subject to Lateral Loading

Self-supported direct-embedded poles are widely used by the utility industry in the United States to support high-voltage transmission lines. For a typical transmission pole, the lateral loads caused by wind and ice loadings govern the design of the pole and foundation. Recent research findings reveal that the methods used in current practice do not yield consistently reliable pole foundation embedment depths in all soil types and for all possible pole classes, lengths, species, and pole loading scenarios. In order to generate improved design methods for transmission pole foundations, validated methods for analyzing laterally loaded piles have been incorporated into the current study. New reliable methods to design safe and cost-effective transmission pole foundations, incorporating both soil and pole properties, are proposed and recommendations are made in rigorous and simplified forms such that they can be easily adopted for use in the utility industry. This study found that the current methods for dete...

Effect of Critical Contact Area Ratio on Moment Capacity of Rocking Shallow Footings

The rocking of a relatively rigid footing on soil c an be visualized as a moving contact problem, with a contact area moving from one side of the footing to the other as the footing rocks. Thus the partial se paration of footing (uplift) and the resulting moment capacity can be more closely relat ed to the critical contact area ratio, A/Ac (ratio between the actual footing area (A) and the area required to support the vertical and shear loads (Ac)). This paper compares th moment capacities calculated by using A/Ac with those obtained from centrifuge a nd 1-g experiments conducted on rocking shallow footings for a range of A/Ac values . It is shown that the moment capacity of a rocking footing is well defined and, unlike bearing capacity, moment capacity is less sensitive to the uncertainty in so l pr perties as A/Ac increases.

Flood of the Red River Basin in 2009 and Effectiveness of Rapid Mitigation Efforts

2009, the city government ordered a mandatory evacuation of the residents living in certain areas of the city, and public schools, including three universities in the region, were closed for up to two weeks. The Red River originates at the Bois de Sioux and Otter Tail rivers in the northern United States and flows through Fargo and Grand Forks, North Dakota, toward Winnipeg, Canada. The river is 885 km long, including 635 km in the United States and 255 km in Canada Minnesota Department of Natural Resources 2009. Given that the U.S. Midwest is geographically flat, the Red River Basin may be the critical floodplain. Thus, moderate floods of the Red River Basin have regularly occurred during the past 110 years. The peak was the 1897 flood that recorded a crest of 12.2 m Flood Information Center FIC 2009. Fargo is the largest city in North Dakota with a population of approximately 100,000 U.S. Census Bureau 2010. The Red River flows along the east side of the city, as shown in Fig. 1. This forum discusses the 2009 flood of the Red River Basin in the city of Fargo and the effectiveness of the rapid efforts to minimize the flood damage. Of particular interest are the forensic investigations into the extreme event, which attributed the flood to four major sources: the sudden change of temperature, snow melting, topography, and soil properties. Postflood activities are briefly discussed.

Transmission Pole Foundations: Alternate Design Methods for Direct-Embedded Round, Wood Transmission Poles

Although close attention is paid to the design of transmission poles, many times the design of the foundation is left up to a rule of thumb method. Reliable and established methods for analyzing laterally loaded piles have been incorporated into the current study to calculate the required depth of embedment for transmission poles, and the results are compared to the current methods. The results show that the current methods for determining embedment depths for direct-embedded transmission poles significantly underestimate or overestimate the required embedment depth depending on the soil conditions. Recommendations are made for alternate design methods for transmission pole foundations. A case study is presented where direct-embedded wood transmission poles fell over due to inadequate foundation design. The results of the case study are compared to the methods presented in this paper. It is concluded that the alternate design methods will generate more accurate results than the current methods.

Development of Innovative Foundation Systems to Optimize Seismic Behavior of Bridge Structures

Preliminary results from a study to develop innovative bridge foundations to optimize bridge performance under earthquake events are presented. Numerical models of bridges with both flexible and stiff footings are compared to demonstrate the potential importance of soil-footing stiffness on the performance of a soil-footing-column-deck-abutment system. Detailed numerical models were developed to capture the inelastic behavior of soil-footing systems. This article summarizes two types of foundation models developed using the OpenSees computational platform. One model uses a contact interface model, soilFootingSection2D, to simulate the foundation and has been proven to be effective in analyzing the cyclic response and displacement of soil-foundation-bridge system. The other uses 2-D nonlinear Winkler foundation consisting of various constitutive springs. Although the former model is more detailed and fundamentally sound in modeling the footings, in its current state it is limited to 2-D use only. The latter model, once verified via comparison to experimental data, can be extended to 3-D. Future work will use the 3-D nonlinear footing models to more accurately simulate the 3-D response of a bridge system to 3-D ground motions.