Structural dynamics of modular bridge expansion joints resulting in environmental noise emissions and fatigue

University of Technology, Sydney. Faculty of Engineering.Whilst the use of expansion joints is common practice in bridge construction, modular bridge expansion joints are designed to accommodate large longitudinal expansion and contraction movements of bridge superstructures. In addition to supporting wheel loads, a properly designed modular joint will prevent rain water and road debris from entering into the underlying superstructure and substructure. Modular bridge expansion joints (MBEJs) are widely used throughout the world for the provision of controlled pavement continuity during seismic, thermal expansion, contraction and long-term creep and shrinkage movements of bridge superstructures and are considered to be the most modern design of waterproof bridge expansion joint currently available. Modular bridge expansion joints are subjected to more load cycles than other superstructure elements, but the load types, magnitudes and fatigue-stress ranges that are applied to these joints are not well defined. MBEJs are generally described as single or multiple support bar designs. In the single support bar design, the support bar (beam parallel to the direction of traffic or notionally parallel in the case of the swivel joist variant) supports all the centre beams (beams transverse to the direction of traffic) using individual sliding yoke connections (for the swivel joist variant, the yoke connection is characterised as a one-sided stirrup and swivels rather than slides). In the multiple support bar design, multiple support bars individually support each centre beam using a welded connection. Environmental noise complaints from home owners near bridges with modular expansion joints led to an engineering investigation into the noise production mechanism. It was generally known that an environmental noise nuisance occurred as motor vehicle wheels passed over the joint but the mechanism for the generation of the noise nuisance has only recently been described. Observation suggested that the noise generation mechanism involved possibly both parts of the bridge structure and the joint itself as it was unlikely that there was sufficient acoustic power in the simple tyre impact to explain the persistence of the noise in the surrounding environment. Engineering measurements were undertaken at two bridges and subsequent analysis led to the understanding that dominant frequency components in the sound pressure field inside the void below the joint were due to excitation of structural modes of the joint and/or acoustic modes of the void. This initial acoustic investigation was subsequently overtaken by observations of fatigue induced cracking in centre beams and the welded support bar connection. A literature search revealed little to describe the structural dynamics behaviour of MBEJs but showed that there was an accepted belief amongst academic researchers dating from around 1973 that the loading was dynamic. In spite of this knowledge, some Codes-of-Practice and designers still use a static or quasistatic design with little consideration of the dynamic behaviour, either in the analysis or the detailing. In an almost universal approach to the design of modular bridge expansion joints, the various national bridge design codes do not envisage that the embedded joint may be lightly damped and could vibrate as a result of traffic excitation. These codes only consider an amplification of the static load to cover sub-optimal installation impact, poor road approach and the dynamic component of load. The codes do not consider the possibility of free vibration after the passage of a vehicle axle. Codes also ignore the possibilities of vibration transmission and response reinforcement through either following axles or loading of subsequent components by a single axle. What the codes normally consider is that any dynamic loading of the expansion joint is most likely to result from a sudden impact of the type produced by a moving vehicle ‘dropping’ onto the joint due to a difference in height between the expansion joint and the approach pavement. In climates where snow ploughs are required for winter maintenance, the expansion joint is always installed below the surrounding pavement to prevent possible damage from snow plough blades. In some European states (viz. Germany), all bridge expansion joints are installed some 3-5mm below the surrounding pavement to allow for possible wear of the asphaltic concrete. In other cases, height mismatches may occur due to sub-optimal installation. However, in the case of dynamic design, there are some major exceptions with Standards Australia (2004) noting that for modular deck joints “…the dynamic load allowance shall be determined from specialist studies, taking account of the dynamic characteristics of the joint…” It is understood that the work reported in Appendices B-E was instrumental in the Standards Australia committee decisions. Whilst this Code recognizes the dynamic behavior of MBEJs, there is no guidance given to the designer on the interpretation of the specialist study data. AASHTO (2004), Austrian Guideline RVS 15.45 (1999) and German Specification TL/TPFÜ 92 (1992) are major advancements as infinite fatigue cycles are now specified and braking forces considered but there is an incomplete recognition of the possibility of reinforcement due to in-phase (or notionally in-phase) excitation or the coupled centre beam resonance phenomenon described in Chapter 3. This thesis investigates the mechanism for noise generation and propagation through the use of structural dynamics to explain both the noise generation and the significant occurrence of fatigue failures world-wide. The successful fatigue proofing of an operational modular joint is reported together with the introduction of an elliptical loading model to more fully explain the observed fatigue failure modes in the multiple support bar design

Noise and disturbance caused by vehicles crossing cattle grids: comparison of installations

Cattle grids are used on roads and tracks to prevent grazing animals from leaving an open space without fencing onto a more controlled area where access to the road from surrounded land is more limited. They are widely used in the UK at the entrances to common and moorland areas where animals are free to roam, but also on private drive entrances. Typically, they consist of a series of metal bars across the road that are spaced so that an animal’s legs would fall through the gaps if it attempted to cross. Below the grid is a shallow pit that is intended to further deter livestock from using that particular crossing point. The sound produced as vehicles cross these devices is a characteristic low frequency “brrrr” where the dominant frequencies relates to the bar passage frequency under the tyres. The sound can be disturbing to riders and their horses and walkers and residents living close by as evidenced by press reports and the need to consider noise aspects in planning for new installations. For this reason and due to the lack of available information on the size and nature of the problem measurements and recordings have been made at a number of sites in Yorkshire in the UK. In addition, questionnaire surveys of residents living close by and façade measurements have also been used to gauge impact. Results show that there is a wide variation in the maximum noise level produced by cattle grids of apparently similar design. This can be related to impact noise produced by the movement of all or part of the grid as the frame comes under impulsive loading as the vehicle crosses. It was further established that some residents living close to the cattle grids were disturbed by the noise, and in some cases vibration, and wanted them removed or suitably modified

Establishing compliance of steel mill products : a comparison between Australian steel standards and the corresponding European standards

Steel bridge design as well as other steel structures design could be considered incomplete unless the compliance of the procured steel has been evaluated and determined through a method which is acceptable in accordance with the requirements of the relevant standard. According to Australian structural steel standards, the acceptance of steel is conditional on the evidence of compliance provided in the mill test report/certifi cate. By comparison, the corresponding European steel product standards include a more comprehensive section explaining the process of evaluation of conformity. This includes a normative section regarding initial type testing, factory production control as well as an informative section regarding a system of attestation of conformity by an approved body and affi xing of CE marking on the product by the steel manufacturer. Also, there are provisions in Australian and European standards regarding the method of establishing compliance as the basis of design. However, a lack of adequate statistical data on overseas manufactured steels poses diffi culties in the derivation of design values of material or product properties by testing

Establishing compliance of steel mill products : a comparison between Australian steel standards and the corresponding American standards

Australian steel Standards have stringent requirements in regard to product conformity. According to Australian structural steel standards, the acceptance of steel is conditional on the evidence of compliance provided in rigorous mill test reports/certificates. Also, Australian structural steel Standards have a mandatory Appendix in regard to product conformity which has been recently supplemented with a scheme for the certification of products by the Australasian Procurement and Construction Council Inc (APCC) and the Joint Accreditation System of Australia and New Zealand (JAS-ANZ). By comparison, the corresponding American steel Standards are industry voluntary standards unless they are cited in government regulations or in a contract. Various industries stipulate mill test reports or reports of tests made by the fabricator or a testing laboratory as evidence of conformity with one of the relevant industry standards such as ASTM, ASME, AISI, SAE and API. However, product conformity is supported by a rigorous legal framework noted in the contracts rather than the product standard. Australian Road authorities need to be familiar with the differences between the Australian and American approach to product conformity in order to comply with the obligation of “duty of care”. A breach of which could result in legal liability

Modular joint testing for the Hunter Expressway

Modular bridge expansion joints (MBEJ's) are widely used throughout the world for the provision of controlled pavement continuity during seismic, thermal expansion, contraction and long-term creep and shrinkage movements of bridge superstructures. Modular Bridge Joint Systems (MBJS) are considered to be the most modern design of waterproof bridge expansion joint currently available. However, there have been numerous observations of fatigue induced cracking in structural beams orientated transverse to the direction of traffic. These beams are, in the English-speaking world, universally referred to as centre beams. However, in Europe the use of /amelia to describe these beams is equally common. Various national and international codes-of-practice have attempted to achieve fatigue resisting designs. Principally, this paper identifies the natural modes of vibration of the single support bar design MBEJ installed into the recently completed Hunter Expressway. Secondly, the paper reports the dynamic amplification factors (DAF) obtained after extensive static and dynamic strain gauge measurements during drive over testing using a tully laden heavy vehicle. Additional quasistatic drive over testing was undertaken using an overloaded heavy vehicle to replicate the AS 5100A160 design axle load. The paper also compares the empirical and theoretical fatigue performance of one of the Hunter Expressway installed single support bar MBEJs when assessed using RMS QA Specification 8316 and the recently ratified European Code ETAG 032

Design strategies for fragment and projectile penetration into steel and concrete structural elements using CONWEP

Designers who design structures to mitigate against blast loadings (Remennikov 2007) have another duty and that is to design for the effects of fragmentation not only caused from bulk explosives, but also impact from projectiles. Impact causes damage to a structure and inevitably results in debris from penetration and perforation (breach) of the structural elements. This debris is in fact the result of the damage outcome to a structure either from the blast loading or projectile impact. Fragmentation (Bangash 2006) is the end result of the blast waves impacting the structural elements resulting in scabbing and spall both of which manifest themselves in the production of fragmentation. This fragmentation is propelled outwards at velocity causing supplementary damage to the structure, adjoining structures and individuals caught near the fragmentation. Those designing for fragmentation must consider many parameters from the geometry of the impacted structural element, to the velocity of the fragments, the weight of the fragments and the range of the fragments. As has been said the fragments cause damage and the designers overall duty is to design to mitigate against damage and death or injury to individuals. The pool of worldwide knowledge on this topic is growing exponentially particularly as the need arises with weapons of high velocity and sophisticated projectiles of extreme lethality and range

Additional structural damage from ground shock as a result of a bombing

The term bombing refers to an uncontrolled demolition (implosion) where a terrorist employs an explosive of a charge weight and detonates it at range and height (air or ground blast) suitable to cause the maximum damage. For a designer trying to design a structure in advance of such a situation happening is extremely difficult thus requiring the consideration of past bombings for the pertinent design parameters. Ground shock is a small earthquake that impacts the structure via energy released from the detonation of the bomb into the ground being converted to wave energy with compression (P) waves, shear (S) waves and the most damaging surface Raleigh (R) waves moving out in all directions from the point of detonation whether it is on or above ground. The common measurement for quantifying ground shock from blast loadings is the peak particle velocity (PPV) as it correlates reasonably well with both building damage and the annoyance levels that people can tolerate under normal circumstances. The Oklahoma City VIED bombing has been used as an example using CONWEP software for a 2200kg VIED detonated at 4.75m from the building. Ground shock results showed that a PPV of 11.5m/s (11500mm/s) was achieved well in excess of guidelines set by AS 2187 and DIN 4150. As well the structure was subjected to radial displacements of 100mm to 350mm adding to the overall damage. Considering the ground shock results along with a reflected overpressure of 51.17MPa it is unsurprising that the building collapsed and many were killed and injured. This is the recommended design overpressure

Review of the basics of state of the art of blast loading

When a high explosive charge detonates in the proximity of an above ground structure, blast waves impact the structure over time and cause different levels of damage and possible collapse of the structure depending on the type of explosive detonated and the size of the charge weight used. Such an event occurs when a building is subjected to an uncontrolled demolition resulting from the actions of an IED. For a structural engineer to design in advance for such an event that must be anticipated at the start of the design process both for the type of explosive and the charge weight that may be used is, to say the least, an extremely difficult proposition considering there are presently no Australian standards or codes to refer to. The blast will see three pressures impact the structure and these are incident pressure (Pso), reflected pressure (Pr) and dynamic pressure (qs) (Ngo et al., Electron J Struct Eng 7:76–91, 2007a). The latter is the smallest of the three whilst the remaining two produce the largest pressures. The question that therefore arises is as to which of the largest pressures to use in designing a structure against blast loadings. Examples exist worldwide as to the outcome of buildings not being designed to carry blast loadings (Yan et al., Eng Fail Anal 51:9–19, 2015) which has inevitably resulted in the total collapse of the structure resulting in death or injury to those unfortunate enough to be caught inside the building as it collapsed. Structural designers design for many loadings such as dead loads, live loads, wind loads, and earthquake loads but the application of blast loads is not the norm and so only carried out in exceptional cases

Review of the most common repair techniques for reinforced concrete structures in coastal areas

Asset managers are faced with the challenge of maintaining concrete structures in coastal environment, within the financial constraints of maintenance budget allocations, such that they remain functionally and structurally safe for the remainder of their design lives. For these reasons concrete remediation is fast becoming an important component of asset management in coastal areas. This research describes remediation techniques and practice currently being employed by prominent public and private organisations responsible for maintaining concrete structures in the lllawarra region (New South Wales, Australia). These common remediation techniques range from conventional restoration, cathodic protection and structural strengthening. The research also considers the underlying factors used to evaluate the effectiveness of these techniques and practices. A model of good practice for concrete remediation in the lllawarra is developed from the literature and industry research undertaken. This model is developed for concrete suffering deterioration caused by the corrosion of steel reinforcement and is aimed to provide intelligent concrete remediation options based on sound principles and industry knowledge