9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310141 PROPOSED METHODOLOGY FOR UPGRADING BRIDGE BARRIERS Vincenzo Colosimo, VicRoads, Australia ABSTRACT The AS 5100 Bridge Design standard (Standards Australia 2007) provides requirements for multiple performance level barriers. Historical barriers constructed before 1970 generally do not meet current standards. This paper builds on ongoing previous research projects within VicRoads which include the VicRoads research report on "Improving existing bridge barriers" (Colosimo 2004a)and the ARRB Conference paper on "Bridge barriers - towards national standards (Colosimo 2006). The report describes typical details of substandard barrier types in Victoria and classifies them into various performance levels. This paper updates details and practices for retrofitting or upgrading bridge barriers by strengthening to the new MASH (AASHTO 2009) heavier test vehicle performance requirements. It also includes updates to the higher performance level barriers as affected by changes in size and mass of local vehicles since the AS 5100 standard implementation as incorporated in the new draft AS 5100 Bridge Design standard (Standards Australia 2014). The paper introduces a methodology for upgrading such barriers by considering both risk and cost aimed at facilitating such improvements. The barrier retrofit upgrading proposals detailed are intended to align with the changing roadside vehicle environment in order to improve roadside safety. INTRODUCTION Bridge barriers designed and built prior to 1970 generally do not meet the current AS 5100 Bridge Design standard Standards Australia 2004 requirements for multiple performance level barriers, with respect to design load and vehicle containment capacity. The older handrail type barriers include poor detailing such as: posts which protrude in front of the rails creating potential traffic snagging hazards; simply supported rails with lack of tensile continuity and end posts exposed to potential traffic impacts.This paper updates results of previous research projects within VicRoads which include the VicRoads research report 834 on Improving bridge barriers(Colosimo 2004a) and the ARRBConference paper on Bridge barriers towards national standards (Colosimo 2006).This paper updates practices by incorporating the new MASH (AASHTO 2009) heavier test vehicle performance requirements as introduced in the new draft for public comment AS 5100 Bridge Design standard (Standards Australia 2014). In addition the paper outlines barrier upgrade options for the higher performance levels. Improvements have been incorporated by making modifications to barriers, in order to produce recognisable multiple performance level barriers. The paper introduces a rational methodology for upgrading such barriers by considering both risk and cost aimed at facilitating such improvements. These measures will reduce the severity of accidents where implemented. EXISTING BARRIERS Existing bridge barriers can be separated into three basic types based on material as: timber, concrete and steel. The older barriers were designed for reduced design loading and could be considered to be architectural handrails rather than traffic barriers. Refer to the following Figures 1 to 10 for typical barriers. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310142 Figure 1:Timber posts on timber bridgeFigure 2:Timber posts on concrete deck Figure3:Concretepoststwinsteeltube rails Figure4:Reinforcedconcretepostsand rails Figure 5: Concrete parapet steel rail Figure6:Concreteendpostandsteelpanels 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310143 Figure 7:Steelposts and guard rail Figure 8: Steel posts with twin steel tube rails Figure 9: Steel posts with twin RHS rail sFigure 10: Steel posts with 3 RHS rails The older pre-1970 designed existing barriers usually fall into the low performance level. Afew more recent barriers, namely the precast concrete parapet plus rail shown in Figure 5 and the steel post plus three rails shown in Figure 10 comply with the current regular performance level. PERFORMANCE LEVEL UPDATE AS 5100 Bridge Standard and new draft AS 5100 changes AS 5100 (Standards Australia 2004) specifies a number of barrier performance levels with the associated design and crash test requirements for each performance level based originally on NCHRP 350 (Ross et al. 1993) test requirements. NCHRP 350 was replaced by MASH (AASHTO 2009) in 2009 which has for some levels, increased test vehicle mass, speed, angle and impact energy as shown in Table 1. This paper also considers similar order updates to the higher performance level barriers as affected by changes in size and mass of local vehicles since the AS 5100 implementation. This paper includes the proposed main changes in the new draft AS 5100 standard, as detailed in Table 2. The barrier upgrading should be designed to contain the updated test vehicles. In brief, justification for barrier upgrading is based on the following factors: The latest AASHTO Manual for Assessment of Safety Hardware (AASHTO 2009) has increased current test vehicle criteria and mass by the order of 10-15 % requiring stronger and marginally higher barriers. This has increased the regular 8 tonne at 80 km/h vehicle to 10 tonne at 90 km/h, the 2 tonne pickup truck to 2.27 tonne and the 0.8 tonne to 1.1 tonne vehicle with a change in impact angle from 20 to 25 degrees. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310144 Table1: Crash test vehicle criteria update for NCHRP 350 to MASH 2009 Local heavy vehicles in Australia have and are continually increasing in mass thus affecting consideration of marginally higher mass trucks for the medium and special (high) performance levels, as follows: oSemi-trailer vehicles have increased from the 42.5 tonne legal to the 45.5 tonne higher high mass limit and Truck-Dog vehicles are currently travelling at 50-57 tonne. oB-doubles have increased from the original 62.5-68.5 tonne. Currently VicRoads is receiving quad axle B-double applications to travel over specific routes at 72.5 -77.5 tonne. oOther high performance freight vehicle applications from industry include 79-85 tonne A-double, 82-90 tonne B-triple and 102.5-113 tonne AB-triple. Similar vehicle mass is currently allowed on roads in the vicinity of Port Melbourne and other specific routes. The trend for vehicle loading to increase will continue and this more than justifies the updating of the design criteria including mass and height in the draft AS5100 ( Standards Australia 2014). oThe design requirements of the bridge infrastructure locally as compared to the USA have also influenced the size and height requirements of bridge barriers. In the USA bridges are currently designed for a light HS20 33 tonne articulated semi-trailer (or 9.4 kN/m uniformly distributed load per lane). In Australia the T44 design vehicle has been a five axle 44 tonne vehicle since 1976 and since 2004 it consists of a SM1600 12 axle (four tri-axle bogie) vehicle plus uniformly distributed load of the order of 160 tonne. The critical constraint to the size and height of vehicles is in part governed by the bridge infrastructure strength and vehicles here are generally heavier and taller than in USA. This trend also justifies the corresponding update in test vehicle requirements and marginal 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310145 (20%) lateral design force increase recommended for the higher barrier performance levels. The AASHTO LRFD Specifications (AASHTO 2012) had updated the design load for the test level 5 (equivalent to the medium performance level) from 500 kN to 550 kN representing the 36 tonne medium mass semi-trailer test vehicle rather than the previous 22tonne rigid vehicle. It should be noted that the British-European practice have relatively basic performance concrete barriers at generally one metre minimum height.The above factors have been considered leading to the following updates in performance test level: vehicle test criteria; lateral force and effective height values for the respective MASH (AASHTO 2009) test level in Table 2. This information is included in the newdraft AS 5100 standard (Standards Australia 2014). Table 2: Recommended crash test vehicle, design mass and effective height Barrier TestLevel Vehi cle Test Criteri a tonne km/hdegrees Lateral Force kN Effective Height metre MASH Test Level Low2.2770251500.62 Regular1090153000.94 Medium3690156001.25 Special(High)441001512001.5~6 Mathematical extrapolation for updates in vehicle test criteria is based on the following: 1.The severity index impact energy being proportional to half of the mass*{speed*sin(degrees)}squared. 2.The low performance force is approximated by the 2 to 2.27 tonne increase in mass. 3.The regular performance force is approximated by the 8 to 10 tonne increase in mass. 4.The medium performance force is approximated by the 80 to 90 km/h speed squared. Note: This update by coincidence is also equivalent to the impact energy from the heavy Euro - British standard CEN H4b test level for a 38 tonne vehicle at 65 km/h and 20 degrees impact angle. 5.The special high performance mass and height denote a marginal correction to values adopted for the AS5100 2004 bridge standard with regards to consideration of the effect of the rear trailer impact at the 100 km/h speed.Note that for the regular performance, in order to maintain the simple recognizable doubling up of lateral containment force between successive performance levels, it is considered that the increase of impact energy due to the speed change from 80 to 90 km/h will be absorbed by an l increase in barrier deflection for metal barriers or additional panel deformation for the rigid barriers. It is also of interest to note that the new lateral design forces are roughly in line with the original design loads stipulated by the historical AASHTO Specification 1989 (AASHTO 1989) shown in brackets in (kN) as follows: Low 150 (134); Regular 300 (356); Medium 600 (624). Anal ysis 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310146 The methodology for analysing current deficient bridge barriers for performance and then designing retrofit upgrading is provided in the current AS 5100 Standard (Standards Australia 2004), the draft AS 5100 Standards Australia 2014) and the AASHTO LRFD Bridge Specifications (AASHTO 2012) including the 2007 edition. This paper has considered the Table 2 changes and updated the barrier upgrade details where necessary.In order to ensure that the rails redirect the test vehicles effectively from the body, wheel and truck floor, an attempt was made historically to provide rails at appropriate positions as indicated in the AASHTO Guide Specifications (Figure A1 Concept A) (AASHTO 1989) as shown in Figure 11.The actual loading pattern from current test vehicles should be considered for new designs. Figure 11: Bridge loading pattern Note that for the current AS 5100 (Standards Australia 2004) the barrier design loadings adopted from the AASHTO Specifications (AASHTO 1998) were originally proved analytically as formulated by HIRSH (1986). The formulation for average force at 100 milli-second average (equivalentto the maximum force divided by 1.5) had to incorporate an additional multiplier of two as shown in Figure 12, to correlate with the vehicle impact force at 50 milli-second as the design load proven by testing. Figure 12: Compari son of vehicl e impact force with weight 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310147 UPGRADING EXISTING BRIDGE BARRIERS Most of the pre-1970 bridge barriers consisted of low light handrail panel systems suitable for upgrading to the low level performance. This can be done by the provision of a continuous rubbing guardrail in front of the existing barrier. The containment capacity of these barriers can be considered as being low performance to the draft AS 5100 Bridge design. Note that the MASH test vehicle for low performance needs to have the guardrail raised in the order of an additional 50 mm above the reference traffic surface. This requirement was also confirmed by Dr. Roger Bligh of the Texas Transportation Institute in J uly 2011 by his presentation at the offices of both the RMS NSW and VicRoads. They had carried out full scale testing of the traditional guardrail (similar to the VicRoads type B guardrail) with the centre of the guardrail at 550 mm above the reference surface, which proved to be unsuccessful for the new MASH requirement for height and mass. In practice this could mean that the stronger Type A guardrail shown in Figure 13 as extracted, from the Country Roads Board standard drawing (CRB 1980) compared to the current Type B (as used by VicRoads since the 1980s) would now provide for this requirement. The post should be redesigned to the current loading and the posts should be spaced at two metre centres. The barrier should then be tested by prototype or simulation testing to the approval of the relevant authority jurisdiction (or based on alternative MASH 2009 manual tested products). Figure 13: Steel Beam Guard Fence Type A (CRB 1980) The substandard railings can be substantially improved in containment capacity by retrofitting rubbing rails with or without additional posts. Typical upgrading treatments, for some types of existing deficient barriers are detailed in this paper. Upgrading modifications are included or described to fulfil the new performance levels. For more comprehensive retrofit upgrading options refer to the Colosimo V. Austroads paper (Colosimo 2004b). Note that the figures for the following upgrades are in part based on prior treatments recommended in the references but now incorporate essential updates where necessary. The updates ensure that they match the updated requirements for the MASH (AASHTO 2009) and the draft AS 5100. Changes made include the guardrail height, cross section geometry, steel sections, size etc. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310148 Standard Timber Handrail The option for timber structures is essentially a guardrail acting as a tensile rubbing rail, based on the strong beam-weak post principle. The new double nested guardrail shown in Figure 14 replaces the existing timber rails thereby reducing snagging and spearing aspects of the existing railing, while providing tensile continuity for redirecting light vehicles. The guardrail section can continue off the structure to the typical guardrail approach treatment.This arrangement incorporates additional timber posts midway between the existing posts which strengthens the barrier and improves its re-directional capacity. Two extra large washers are required for each bolt through timber, to minimise the potential for punching through the timber. The capacity of the guardrail can be marginally improved, by replacing the existing undersized timber posts (152 mm x 102 mm) with larger 175 mm x 125 mm hardwood sections, and increasing the size of connecting bolts. The performance level for this arrangement due to its low height is Low. It is recommended that this design should also be proven by testing prior to its wider adoption. Figure 14: Standard timber handrailBarrier Improvement Tubular Grille Barrier The option in Figure 15 provides a rubbing guardrail, to avoid the potential for snagging of the existing system and improve vehicle redirection. The existing rails should be made continuous by butt welding to minimise the creation of loose projectiles during vehicle impacts. The system is strengthened to a regular performance level by the addition of an additional steel hollow section rail (to be designed and tested as required by the relevant authority jurisdiction). Double nested9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 2310149 Figure 15:Steel tube gri ll eBarrier Improvement Metal Grille BarrierThe option shown in Figure 16 provides a continuous rubbing guardrail to avoid the potential for snagging of the existing system and thus improve vehicle redirection. This treatment is similar to that described for the tube grille barrier. The system may also be strengthened to a regular level performance by retrofitting two square hollow section rubbing rails. Figure 16: Metalgrill e Regular l evel improvement BARRIER STRENGTHENING OPTIONThe barrier options shown in Figure 8 and Figure 9 are intended to be at the traditional low performance level of the AS 5100(Standards Australia 2004). Marginal upgrading to achieve continuity of the steel rails can achieve the requirements of the MASH (AASHTO 2009) low test level. The discontinuous simply supported rails can be made continuous by butt welding the rails together for improved tensile behaviour. This will improve both the containment capacity as well as increase the effective height of the barrier. Over the expansion joints continuity splices need to be designed and introduced as per the AS 5100 (Standards Australia 2007) and its new draft (Standards Australia 2014). 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 23101410 BARRIER REPLACEMENT OPTIONS Barrier replacement improvements have been reported in (Colosimo 2004b). A typical example for concrete bridges is shown in Figure 17. If it is considered that complete replacement of an existing deficient barrier is warranted, then a new barrier may be adopted or the proposal shown in Figure 17 may be utilised to fulfil the regular level performance. This is particularly suitable for sites that incorporate a guardrail approach treatment. This barrier needs to be proof designed and approved (possibly subject to at least simulation testing) as required by the relevant jurisdiction. This arrangement can also be considered as an alternative strengthening to options like those of Figures 15 and 16 in where the rubbing rails may not provide economically the effective height for the regular performance level. A marginally modified arrangement of that shown in Figure 17 with shorter posts and base plates fixed in front of the existing grille barrier can be designed for the regular performance. The existing grille barrier provides the pedestrian balusters and some restraint to the test vehicle impact. The alternative to this arrangement would be to incorporate three steel hollow sections as shown in Figure 10. Considerable progress has already been made in developing some proposed standard barriers. Some proposals for the various performance levels are shown in Colosimo (2009) on recommended higher performance bridge prototype barriers. The higher performance barriers warrant prototype testing prior to them being considered for national use. Figure 17: Concrete bridge deck repl acement optionMETHODOLOGY FOR RETROFIT UPGRADING BARRIERS The methodology should incorporate three stages including bridge selection, barrier performance level and upgrading priority.Bridge Selection Bridge selection should be based on the following: 1.Road classification in regards to transportation needs such as heavy permit vehicles and commercial vehicles. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 23101411 2.Age and type of barrier with emphasis on the older pre -1970 bridges with handrail type barriers as detailed in this paper.3.Site risk factors affecting barrier performance deficiency such as traffic and commercial vehicle count, type and width of road, alignment, height, gradient, offset of barrier to lane, and under structure land use etc. Refer to the draft AS5100 (Standards Australia 2014) for full details. Performance LevelPerformance level should be based on the following: 1.The required performance level should be determined from the AS 5100 selection procedure based on the site risk factors. 2.Determine by structural analysis the performance of the existing barrier and 3.Determine the performance level upgrade for the bridge barrier. 4.Design the upgrade requirement which could consist of the following alternatives: Guardrail retrofit in front of the barrier including consideration of twin guardrail for additional height effectiveness. The guardrails can be single or double nested for extra strength. The guardrails can also be fixed on steel pivot arms forwards of the existing barrier to ensure that they do not rotate downwards when impacted. One or more cold formed hollow steel sections fixed to the front of the existing barrier with or without separate posts forwards of the existing deficient barrier. An additional post and rail barrier fixed to the top or rear of the existing barrier or parapet. If the retrofit is too complex or too costly consideration can be made to retrofit a new barrier on the bridge structure following removal of the existing barrier. Upgrading PriorityPriority for barrier upgrading should be determined once most of the upgrading sites and relevant cost is available and a benefit risk cost analysis has been carried out to determine the theoretical order for the barrier upgrades. The following factors should be considered in determining priority: 1.The remaining life of the bridge and existing barrier. 2.The accident history if any and associated potential future cost. 3.Site risk as determined for the performance level selection. 4.Historical significance of the bridge as it may influence the type of barrier upgrade and additional cost. 5.The allocation of funding for bridge strengthening which would need to incorporate a new barrier instead of the upgrading. 6.Other factors such as natural disasters which can influence the priority as well. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 23101412 CONCLUSIONS The draft AS 5100 provisions for barriers will facilitate the design, approval and introduction of recognisable standard barriers for multiple performance level criteria. This will improve road safety and minimise litigation issues in respect to bridge barriers. The upgrading proposals detailed in this paper have been developed and updated, to provide suitable strengthening measures for typical types of deficient barriers in use and reduce hazards caused by protruding posts.Strengthening proposals are based on the provision of a smooth continuous steel railings or high strength guardrail continuous with the approach guardrail. Alternatives to strengthening involving more costly replacement barriers are also considered. A methodology for retrofit upgrading of deficient bridge barriers is detailed in order to assist the relevant authority jurisdiction to select and upgrade when possible in order to mitigate risk economically It is proposed that barrier systems and barrier retrofit upgrades as detailed in this paper with minor improvements, additional design and testing when required may be considered for future barrier upgrades. ACKNOWLEDGEMENT The author wishes to thank the Chief Executive of VicRoads Mr. J ohn Merritt for his permission to publish this paper and acknowledges the contribution provided by other staff from the VicRoads Structures Group including Sukie Shen for their assistance in providing proof analysis of minor barrier modifications. The views expressed in this paper are those of the author and do not necessarily reflect the views of VicRoads. REFERENCES AASHTO 1989, Guide specification for bridge railings, American Association of State Highway and Transportation Officials, Washington DC, USA. AASHTO 1998, LRFD Bridge Design Specifications, 2nd Edition, American Association of State Highway and Transportation Officials, Washington, D.C. 20001. AASHTO 2012, Bridge design specifications, 6th edn, American Association of State Highway and Transportation Officials, Washington DC, USA. Standards Australia 2007, AS 5100 Bridge Design, Standards Australia. Standards Australia 2014, Draft AS 5100 Bridge Design, Part 2 Design loads, Standards Australia. Colosimo V. 2009, Recommended higher performance bridge prototype barriers 7th Austroads Bridge Conference, New Zealand. Colosimo V. 2006, Bridge barriers towards national standards, 22nd ARRB Conference, Perth. Colosimo V. 2004a, Improving Existing Bridge Barriers, VicRoads research project report 834, VicRoads, Melbourne. Colosimo V. 2004b, Bridge Barriers Implementing theAS5100 Bridge Design Code Provisions, 5th Austroads Bridge Conference, Hobart, Tasmania. CRB. 1980, Book of Standard Drawings for Roadworks, Country Roads Board, Melbourne. Ross, HE , Sicking, DL,Zimmer, RA & Michie, J D 1993, Recommended procedures for the safety performance evaluation of highway features, NCHRP report 350, Transportation Research Board, Washington DC., USA. AASHTO 2009, Manual for assessing safety hardware (MASH), American Association of State Highway and Transportation Officials, Washington DC, USA. 9th Austroads Bridge Conference, Sydney, New South Wales 2014 ABC2014 Proposed Methodology for upgrading bridge barriers VC 23101413 HIRSH, T.J . 1986, Longitudinal barriers for buses and trucks, Symposium on geometric design for large trucks, Texas Transportation Institute, Transportation Research Record 1052. AUTHOR BIOGRAPHY Vincenzo Colosimo is an Engineer in the Structures Group of Technical Services within the Operations Division of VicRoads. He joined the organization in 1966 and has extensive experience in the design of bridges and associated road structures.Other experience includes road design and bridge construction. He is currently the Manager Bridge Assessment, responsible for coordinating heavy load permit vehicle bridge assessments, making bridge load rating recommendations to the Principal Bridge Engineer and making recommendations for the approval of new commercial vehicles by VicRoads. He has been involved with research, testing, and developmental work associated with standardization of components for bridge and road structures. He has acquired extensive expertise in bridge furniture with a particular emphasis on road safety barrier developments. He also provides specialist support to other areas of VicRoads and external organizations. Copyright Licence Agreement The Author allows ARRB Group Ltd to publish the work/s submitted for the 9th Austroads Bridge Conference, granting ARRB the non-exclusive right to: publish the work in printed format publish the work in electronic format publish the work online. The Author retains the right to use their work, illustrations (line art, photographs, figures, plates) and research data in their own future works The Author warrants that they are entitled to deal with the Intellectual Property Rights in the works submitted, including clearing all third party intellectual property rights and obtaining formal permission from their respective institutions or employers before submission, where necessary.