Jerry Wekezer

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.

Assessment of passenger security in paratransit buses

The main objective of this study was to assess usefulness of 3-D, nonlinear dynamic, explicit computer codes for transit safety and security research. An analysis of response of a paratransit bus structure under loading caused by high explosive (HE) detonation is presented. It was assumed that the cubic HE charge detonates in the air near the bus. The ground was modeled as a rigid stationary wall. The problem was studied using LS DYNA, an explicit, 3-D, dynamic, nonlinear finite element program. The HE detonation and the processes of shock propagation in the air were modeled using the mesh with the Euler’s formulation. The Euler’s mesh was modeled as a rectangular prism sufficiently large enough to cover the entire bus structure. The nonreflecting boundary conditions on the top and side surfaces of the Euler’s domain and the sliding interface on the bottom side for the contact with the ground were assumed. A finite element model of the Ford Eldorado Aerotech 240 paratransit bus was developed for this study. This model consisted of 73,600 finite elements and had 174 defined properties (groups of elements with the same features) and 23 material models. Computational analysis provided useful information about dynamic deformations and damage inflicted to the bus structure under load blast wave activated by the HE detonation. It allowed for detailed, rigorous analyses of time histories of accelerations, velocities, deformations, and stresses. Resulting acceleration and overpressure histories were correlated with expected blast injuries of the bus passengers. The data obtained can be used to improve passenger safety and to reduce the threat of suicidal terrorist attacks against public transit. Changes in the bus structure and replacement of some materials to build a safer class of vehicles can be carefully considered and implemented.

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.

Structural Response of Paratransit Buses in Rollover Accidents

Abstract Existing crashworthiness standards in the United States are focused primarily on passenger cars and school buses, while paratransit buses are not required to meet these codes. The main objective of this research was to develop a finite element (FE) model of the Champion Challenger paratransit bus in order to perform the crashworthiness evaluation during the rollover test using computational mechanics. The FE model was developed based on technical description and AutoCAD files of the bus structure supplied by Champion, the producer of the Challenger bus. In the absence of U.S. crashworthiness standards applicable to paratransit buses, the FE model of Champion Challenger bus was used for computational mechanics study of the rollover test according to ECE Regulation 66. All numerical analyses were carried out using LS-DYNA, a nonlinear, explicit code. Experimental validation of assumed material models, mesh density, and contact definition was performed through a simple pendulum impact test of the bus sidewall panels [1].

FINITE-ELEMENT MODELING OF G2 GUARDRAIL

A finite-element model of the AASHTO G2 guardrail (weak-post W-beam) was developed and analyzed under vehicle impact conditions by using LLNL-DYNA3D, a nonlinear, explicit, three-dimensional, public-domain, finite-element code. The modeling procedures and problems encountered are described, and suggestions for further research are given. W-beam and S3 X 5.7 steel post mesh optimization procedures and results are described. A suitable point of fixity for the posts to account for soil effects is determined. W-beam-to-post connections were investigated by three different methods. Impact influence lengths and problems associated with modeling flexible barriers are discussed. The steps taken to assemble a model, including a prebuilt vehicle model, are given. The G2 guardrail was struck with the 820C vehicle model, developed by FHWA, at a speed of 26.69 m/sec (59.7 mph) and an angle of 15.4 degrees.

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.

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.

Testing Program for Crashworthiness Assessment of Cutaway Buses

The State of Florida acquires over 300 cutaway buses every year. The increasing popularity of such buses raised concerns about passenger safety and overall crashworthiness of this transportation mode. An extensive research program was initiated at Crashworthiness and Impact Analysis Laboratory (CIAL) to facilitate experimental testing and computational mechanics as two integral parts for crashworthiness evaluation of the cutaway buses. The major objective of the evaluation program is to ensure that bus structures perform well during actual accidents, especially rollovers. Multi-level testing program includes testing of: small samples for material characterization, larger passenger compartment connections, impact testing of wall panels, as well as full scale roll-over and side impact tests of the inspected vehicles. Due to dynamic nature of rollover accidents, the program was originally based on dynamic testing. However, further research led to introduction of several simpler yet equivalent, quasi-static tests. Testing data is also used to support verification and validation of detailed finite element models of the buses, which are developed for LS-DYNA—an explicit, non-linear finite element solver. The program was well received by cutaway bus industry and it resulted in strong commitment and collaboration with bus manufacturers.

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)