Leslaw Kwasniewski

Experimental Assessment of Dynamic Responses Induced in Concrete Bridges by Permit Vehicles

Results from experimental testing of three permit vehicles are presented in the paper. The selected heavy vehicles, which require permits from state DOTs, included two tractor-trailer systems and a midsize crane. The vehicles were experimentally tested on popular existing speed bumps and on a representative highway bridge. The selected bridge was a reinforced-concrete structure constructed in 1999, located on the U.S. 90 in Northwest Florida. The bridge approach depression, combined with a distinct joint gap between the asphalt pavement and the concrete deck, triggered significant dynamic responses of the vehicle-bridge system. Similar dynamic vibrations were observed and recorded when the permit vehicles were driven over the speed bumps. Time histories of relative displacements, accelerations, and strains for selected locations on the vehicle-bridge system were recorded. The analysis of experimental data allowed for assessment of actual dynamic interactions between the vehicles and the speed bumps as well as dynamic load allowance factors for the selected bridge.

Material and structural crashworthiness characterization of paratransit buses

Abstract A comprehensive experimental material characterization and full-scale testing of structural connections of paratransit buses is presented in this paper. Structure-property relations were quantified for the constitutive material models used for finite element simulation-based crashworthiness research of paratransit buses. Several structural materials used by the paratransit bus industry were identified, and coupon size specimens were tested. A dynamic wall panel test with an impact hammer provided validation data for the finite element simulations. In addition, quasi-static laboratory tests of standard connections between the walls, floor, and the roof of a selected paratransit bus were performed. In addition to FE model validation, the connection testing allowed for thorough qualitative assessment of connection design, which resulted in improved crashworthy connection details. The experimental materials characterization and validation protocol described in this paper is consistent with the draft of the crash and safety standard for structural assessment of paratransit buses in the state of Florida. This roadmap is intended to be used for crashworthiness evaluation of future paratransit buses.

Dynamic Interaction Between Heavy Vehicles And Speed Bumps.

The paper presents finite element (FE) model development and experimental validation for a truck tractor with a three axle single drop lowboy trailer. The main objective of this research activity was to create a simplified, three dimensional virtual FE model, applicable for computer simulation of dynamic interaction between a vehicle and a bridge or road structure. Such model should provide a reliable approximation of dynamic loadings exerted by the wheels to the bridge or pavement structure for a wide range of total weights and speeds considered. To meet this requirement the FE model should have correct mass distribution and properly represented stiffness characteristics of the suspension system. As explicit laboratory testing of the suspension system requires its disassembling and is very expensive, an indirect method was applied to find the stiffness and damping characteristics of the suspension. The study reported in this paper consists of experimental and numerical parts. During the experimental tests the vehicle was driven across the speed bumps at different speeds. The relative displacement and acceleration histories were recorded for several points located on the vehicle axles and the frame. In addition, a speed bump was scanned on site using a laser scanner. The experimental data was subsequently used for the development and calibration of the spring and damping characteristics for suspension systems of the FE model. The numerical part was based on non-linear, explicit, dynamic, finite element (FE) analysis using the LS-DYNA computer code.

Principles of Verification and Validation

This paper discusses the concepts of verification and validation in computational mechanics with special attention to structural fire engineering, by referring to recently published papers and guides on V&V that define some best practices and show directions for future development. The perspective of an analyst, who develops computational models, makes runs, and analyses numerical results mostly using software based on the finite element method, is presented. The considerations emphasize practical problems encountered in the V&V process, potential sources of errors and uncertainties, the importance of sensitivity study, new ideas regarding the relationship between validation and verification, differences between calibration and validation, new aspects of the validation metrics, and guides for designing validation experiments. The discussion is illustrated by computational problem examples.

Comprehensive rollover testing of paratransit buses

The paper presents verification and validation procedures for the originally developed FE model of a paratransit bus, which was built for rollover test simulation. Verification of the FE model is primarily performed through analysis of the energy balance during rollover test. Series of validation experiments were designed and performed in hierarchical (multi-scale) manner. The verified and validated FE model was used to perform sensitivity analysis of the bus response to changes in material properties as well as initial conditions of the test. A measure named Deformation Index (DI) was proposed as a new quantifier of the overall deformation for easier interpretation and comparison of the rollover test results. Safety margin of the bus is estimated based on this new concept.

Numerical Study of Joint Behaviour for Robustness Assessment

The paper presents studies on numerical modelling of beam-to-column joint behaviour in typical service and exceptional design situations. The complexity of such investigations arises from highly nonlinear effects associated with the prediction of joint performance, such as structural imperfections, large displacements and rotations, inelastic properties of steel and concrete, bonding effects between steel and concrete, and slip between concrete and structural steel, among others. The paper addresses these problems and provides validation of numerical modelling techniques trough comparison with experimental data for joints under hogging and sagging moments.

Virtual Tests on Axially and Rotationally Restrained Steel Column Under Fire

During a fire, some additional forces are imposed on columns due to varied thermal deformations in the neighboring structural components. Axial and rotational restraints can produce substantial loadings, which together with thermally reduced stiffness, can lead to its premature buckling and reduction of the column fire resistance. The paper presents a study on numerical modeling of steel columns subjected to prescribed axial and rotational restraints and time dependent temperatures. The problem is investigated using nonlinear finite element simulations carried out using the general purpose program LS-DYNA®. The paper focuses on model development and its verification and validation. Several modeling options and strategies for modeling thermal and mechanical boundary conditions have been considered. A numerical prediction of structural response during heating is compared with published experimental data.

Example Validation of Numerical Modeling of Blast Loading

This paper reports a follow-up feasibility study on different approaches for numerical modeling of blast loads, implemented recently in a few commercial programs based on finite element method and explicit time integration. Four approaches have been considered including: explicit blast wave representation using fluid-structure interaction (FSI) with 2D and 3D multi-material arbitrary Lagrangian-Eulerian (ALE) formulations, direct application of empirical explosive blast loads on structures, and the most recent, combined method, in which direct empirical loading is applied to a reduced ALE domain. Each of these approaches has its own strengths and weaknesses, although the last one seems to be the most universal. Based on the published experimental data, a benchmark problem was selected, which considers a pressure loading exerted by explosion of near field hemispherical charges on a rigid steel plate. The comparison is done in terms of pressure peaks (overpressure) and time histories of reflected pressure, and reflected specific impulses.

Safety assessment of wheelchair occupants in paratransit buses

Safety assessment of passengers with disabilities travelling in their wheelchairs in paratransit buses is presented. Computational mechanics and LS-DYNA non-linear finite element code were used as tools in this study. All finite element models were partially validated using data available from experimental sled tests. The validated dummy-wheelchair-bus system, which was developed, allowed for quantitative assessment of injury criteria in several accident scenarios. Although backward seating was found beneficial in reducing severity of injuries during accidents, the outcome is sensitive to imperfect initial conditions during accidents. Material presented allows for detailed assessment of benefits and shortcomings of each configuration considered.

Finite Element Analysis Of A Transit Bus

Most of the bus safety standards in the USA are not applicable to cutaway buses for which a production process is split into two stages. First, the chassis and cab section are assembled by automobile manufactures. Then the vehicle is shipped to another company, where bus body and additional equipment are installed. Lack of strict structural standards for transit bus body builders stimulates the need for crashworthiness and safety evaluation for this category of vehicles. Such an assessment process is needed and important since transit buses are often used to transport disabled passengers. Although a full scale crash test is considered the most reliable source of information regarding structural integrity, crashworthiness and safety of motor vehicles, the high cost of such tests and difficulties in collecting data result in an increasing interest in the analytical and computational methods, which allow for extensive safety studies once the finite element model is validated. This study focused on a selected transit bus, the Ford Eldorado Aerotech 240. Due to the lack of design data the reverse engineering process was used to acquire the geometric data of the bus. The finite element (FE) model was developed based on the geometry obtained by disassembling and digitizing all major parts of the actual bus. The FE model consists of 73,600 finite elements, has 174 defined properties (groups of elements with the same features) and 23 material models. All parts are connected using different multi point constraints and special links with failure to model actual types of structural connections such as bolts and spot welds. LSDYNA non-linear, explicit, 3-D, dynamic FE computer code was used to simulate behavior of the FE model under different impact scenarios, such as front impact and side impact of two buses at various velocities. Structures Under Shock and Impact VIII, N. Jones & C. A. Brebbia (Editors)