1. INTRODUCTION

In general, loading codes around the world are in close agreement for most loading types, with variations of +/- 20% for comparable conditions. The uniform loadings for handrails, guard rails and grab bars are an anomaly with a factor of 4 between the maximum load in ASCE 7-22 and comparable maximum loads in Canadian National Building Code (CAN), Eurocode (EN), British Standards (BS) and Australian and New Zealand Standards (AS/NZS), and Brazil (ABNT). Comparison of the loads for typical cases have good agreement with 50 lb/ft (0.73 kN/m) versus 0.75kN/m for the distributed loads, however for crowd and stadium loading ASCE-7 and IBC have no additional requirements, whereas CAN, EN. BS, and AS/NZS require 3kN/m (~200 lbf/ft) for stadia. Additionally, EN, BS and AS/NZS also have an intermediate level of 1.5 kN/m for specific areas of assembly, but this is not in the CAN standard. In total, of 45 countries in which balustrade loadings were able to be found at the time of submission: 40 countries have a maximum crowd loading of 3kN or greater; one country (India) has a loading of 2.25kN/m (3x the US code loading) and none have a lower loading.

A historical study of US documents pertaining to loading yields three main reference sources: ASTM E985 Standard Specification for Permanent Metal Railing Systems for Buildings, ASCE/SEI-7 Minimum Design Loads And Associated Criteria For Buildings And Other Structures and International Building Code. Significantly, ASTM E985 was originally approved in 1984, was last updated in 2000, in its references it quotes as sources AS1170 and BS6399, which at the time also showed loadings of ~0.75kN/m. BS 6399 adopted crowd loadings in 1996, AS/NZS in 2002 and EN 1991 in 2002. Without maintenance of standards in the US, balustrade loadings have languished, thus the question comes: ‘why did they change elsewhere, and are those changes justified?’

The load categories proposed here were introduced in BS6399 – 1996, the actual source of which is unknown to the author, however it is possibly a reaction to the 1989 Hillsborough Disaster (UK) in which 96 people died in conditions of overcrowding, following collapse of a crowd barrier at an FA Cup semi-final soccer match. The report by RA Smith notes other precedent collapses. (Smith 1994) Railing collapses have also been reported at a Philadelphia (PA, USA) stadium in 1998 (Styan et al.2007), Maryland (USA) in 2022, and in 2021 at Public University of El Alto in Bolivia, which resulted in at least six deaths and multiple injuries. (Figures 1, 2 and 3 respectively.) The latter item is relevant as the Bolivian loading standard for Actions on Structures (NB 1225002-1) requires 1.0 kN/m, which is greater than ASCE-7. The Philadelphia, Maryland and El Alto events are documented in video.

1998 Philadelphia railing collapse resulting in broken neck.

https://www.youtube.com/watch?v=cBqyJPGZcdc

Other collapses without serious injury include events at NFL football games. These are significant because there is not a great depth of people pressing behind the barrier.

https://youtu.be/C6UdjxWWyUQ

The El Alto balustrade collapse demonstrates the effects of crowd load in assembly area. THe collapse resulted in 7 fatalities.

https://www.infobae.com/america/america-latina/2021/03/02/el-presidente-de-bolivia-lamento-la-tragedia-ocurrida-en-la-universidad-de-el-alto-y-aseguro-que-espera-el-pronto-esclarecimiento-de-los-hechos/

In the United Kingdom, The Hillsborough Disaster in 1989 was thoroughly investigated and is well documented by R.A. Smith from University of Sheffield in “The Hillsborough Football Disaster: Stress Analysis and Design Codes for Crush Barriers”, published in Engineering Failure Analysis (Smith, 1994). In the paper, Smith quotes the investigation report of Lord Tayor, noting that similar investigations had occurred in 1924, 1946 (33 deaths), 1972 (66 deaths), and 1986 (56 deaths). Smith (writing in 1994) also noted other crowd crush events in 1990 (Mecca, 1,426 deaths), 1991 (Shanghai, 105 deaths) and 1992 (Madras,65 deaths). The Wikipedia page https://en.wikipedia.org/wiki/List_of_fatal_crowd_crushes#21st_century summarizes hundreds of events and thousands of deaths due to crowd crushing. Whilst all of these do not include details of barrier collapse, they demonstrate that fatal crowd loading is sufficiently frequent to be a design consideration; we know that if a barrier collapses it is more likely to cause crowd collapse and fatalities. It is important to prevent crowd loading situations turning into fatal ones.

In a report ‘Going Off the Rails’ (Fried et al. 2021), The National Center for Spectator Sports Safety and Security (NCS⁴ at University of Southern Mississippi) notes a history of fatalities and serious injuries at US sporting arenas, both old and new. This report also notes that the effects of alcohol and “horseplay” (rough and boisterous behavior) should be considered in the design of barriers at sporting facilities.

2. DESIGN LOADING FOR BARRIERS

Whilst the Hillsborough Disaster was attributed in part to extreme over-crowding, post-failure analysis indicated that the railing failed at approximately 8 kN/m, thus despite being four times the current design load in ASCE7-22 the recommend in Australian Standard AS1170.1: 2002 of 3.0 kN/m (~200 lbf/ft) are not excessive for reasonable design load situations involving crowds, . The El Alto incident reinforces that elevated rail loading is possible at assembly areas other than stadiums, so the approach in AS/NZS and EN, which is broader than in CAN, is justified. Eurocode includes a range of 3-5kN/m with 3 kN/m recommended. This approach highlights that there are some circumstances in which the designer may wish to select a loading greater than 3 kN/m if it is considered appropriate.

Studies of crowd crush by Fruin (1993) indicated that crush forces of up to 3,430N (766lbs) can be applied to a single person in overcrowding situations, hence similar loads should be anticipated to the barriers that contain crowds. This is important because the collapse of a barrier can lead to people falling over an edge, or falling down and being crushed those that land on top of them.

R A Smith includes the formulation of a ‘leaning crowd’ model used to estimate loads generated on a barrier on a stadium with terraced seating. (Smith, 1994)

An animation at CrowdRisks.com/research.html provides a computer simulation of “crowd collapse”, a situation in which a disturbance causes one person to fall and they are unable to shift and regain balance without pressing on the person next to them, who is then also pushed off balance, creating a domino effect -- with increasing mass and synchronous dynamic effect -- and or multi-cyclic impact as the wave passes through the crowd. Review of the video of the El Alto incident (Figure 3) indicates that there were ‘pressure waves’ within the crowd and that a scuffle added a dynamic component to the static load at the time of collapse.

An Australian Study by C T Styan, M J Masia, and P W Kleeman “Human Loadings on Handrails” in the Australian Journal of Structural Engineering (Styan et al. 2007) takes an experimental approach to measuring the horizontal loads possible on rails and finds that the loads in the BS, EN, AS/NZ standards are reasonable and that in a significant number of cases, exceed the loads in ASCE-7. The study by Styan, Masia and Kleeman also documents other failures due to overloading in the introduction to their study. It notes the investigation of the 1998 Philadelphia barrier collapse was due to overloading, not a design fault, and concludes that this was in a situation of only one to two audience rows deep. Styan et al. also validated loading with full-scale testing with various types of occupancy and compared them with the design loading. In each case, test results showed the design loads were appropriate; the results also found that in circumstances subject to “unruly behavior”, such as kicking the barrier, higher than design loading was possible. The testing confirmed 3.0 kN/m (~200 lbf/ft) for crowds and also confirmed 1.5kN/m (~100 lbf/ft) loading for occupancy with assembly but without crowd loading.

2.1 Proposed Loading for Balustrades

As the occupancy categories used in the US are different than in the other standards referenced, the tables in BS, AS/NZS and EN have been grouped and summarized by load. Notably, in category “A” there is a reduced load relative to ASCE-7 for interior single residential usage. The loading in the US is based on a “grab load” and “soft body slip impact load” as investigated by ANSI, hence reductions are not proposed and the table is a conservative bounding of the criteria.

Table 1: Proposed Balustrade Loads

*Loads are reduced based on ASCE7 and to convenient imperial numbers.

3. FACTORS OF SAFETY AT THE ANCHORS

ASTM E985 continues to be referenced and was recently reinstated in its prior form so that it can be updated. As such, it is noteworthy that not only does it not recognize assembly or crowd loading, it regards the 50 lb/ft as a test load for both the balustrade system and the attachments to structure as tested in ASTM E894 Test Method for Anchorage of Permanent Metal Railing Systems and Rails for Buildings and E935 Test Methods for Performance of Permanent Metal Railing Systems and Rails for Buildings. Such testing protocols do not currently allow any variability in the materials or testing to provide a safety factor. For example, the National Design Specification (NDS) for wood recommends a safety factor of 5 for withdrawal of fasteners relative to test data to allow for system variation. For post-installed concrete anchors under static loading a factor of safety of 4 is common, but is greater for dynamic loading. Post-installed concrete anchors should pass the requirements of American Concrete Institutes’ ACI 355.2 Qualification of Post-Installed Mechanical Anchors in Concrete and Commentary. As noted in a report “Going off the Rails” by The National Center for Spectator Sports Safety and Security, where railings fail, failures at the anchors are the most common cause. The Australian Standard 1170.0 Structural design actions, Part 0: General principles Appendix B provides proof load testing factors based on sample size and coefficients of variation. Following ASTM methods, the combination of lack of crowd loading and safety factor for testing results in metal railing systems attached to a wood structure, tested and approved to ASTM E985 and E935, are one fifteenth of the loads prescribed by AS1170.1 and testing to AS1170.0 Appendix B. Even for the current ASCE 7 design loads, the lack of a safety factor in testing means that systems approved by testing potentially have a significantly lower strength than systems justified by calculation to the relevant materials standards.

4. CONCLUSION

The proposed loads in Table 1 are reasonable and validated. The reference in Eurocode EN 1991 indicates a range of crowd loads between 3 kN/m (200 lb/ft) and 5 kN/m (340 lb/ft) and the post-failure analysis of the Hillsborough barriers indicated failure at ~8 kN/m (550 lbf/ft); however, the latter was in a case of extreme overcrowding which might be considered greater than a reasonable design case. Crowd loading of 3 kN/m (200 lb/ft) has also been adopted by the Canadian code for stadiums.

Justification by testing to meet standards needs to incorporate suitable safety factors based on the materials they are being attached to as well as testing variations. For testing with samples of 6 or more , a proof load factor of 2.5x for steel, 4x for concrete and 5x for wood is consistent with achieving statistical significance consistent with the respective materials’ standards and coefficient of variation.

There is a large discrepancy between balustrade loadings in the United States and most other countries. Changes elsewhere were based on multiple disasters, investigation of those events and validation by testing. The balustrade loads similar to Table 1 have been adopted in over 40 counties. These loads have been proposed to ASTM and ASCE for future incorporation. In the interim, design professionals and project specifiers have the option to follow international best practice when selecting appropriate testing and design loads for balustrades and guards.

5. Appendix

SUMMARY OF BARRIER LOADING (Where Known)

References

ABNT NBR 6120:2010 Norma Brasileira - Design Loads for Structures (translated)

AS/NZS 1170.1 – 2002 Structural design actions - Part 1: Permanent, imposed and other actions

ASCE/SEI 7 – 22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures

BS 6399-1: 1996 Loading for Buildings

BS 6180:2011 Barriers in and about buildings

EN BS 1991-1-1: 2002 Eurocode 1: Actions on structures - Part 1-1: General actions - Densities, self-weight, imposed loads for buildings

National Building Code of Canada, 2015

NB 1225002-1 Norma Boliviana - Actions on Structures - Part 1(translated)

Fried Dr. G., Grant Dr A., Kocak Dr S. “Off the Rails” National Center for Spectator Sports Safety and Security- https://ncs4.usm.edu/research/research-seminar-series/#popup-2

Fruin, J.J. (1993). The causes and prevention of crowd disasters. First International Conference on Engineering for Crowd Safety, London, England, March 1993.

Smith R.A. (1994) “The Hillsborough Football Disaster: Stress Analysis and Design Codes for Crush Barriers”, Engineering Failure Analysis Vol1, No3 pp183-192, 1994 https://www.sciencedirect.com/science/article/pii/1350630794900175

Styan C.T. , Masia M.J. & Kleeman P.W. (2007) Human Loadings on Handrails, Australian Journal of Structural Engineering, 7:3, 185-196, DOI: 10.1080/13287982.2007.11464975, https://doi.org/10.1080/13287982.2007.11464975

Behaviour and Mechanics of Crowd Crush Disasters https://riskfrontiers.com/insights/behaviour-and-mechanics-of-crowd-crush-disasters/

Crowd Collapse Simulations: Crowd Risks.com https://www.crowdrisks.com/research.html

https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.28#:~:text=g)(2)(i).-,1910.28(b),-Protection%20from%20fall

https://riskfrontiers.com/insights/behaviour-and-mechanics-of-crowd-crush-disasters/

https://simplifiedsafety.com/safety-railing/osha-railing/

https://en.wikipedia.org/wiki/List_of_fatal_crowd_crushes#21st_century

Philadelphia railing collapse: https://www.youtube.com/watch?v=cBqyJPGZcdc

Rogers Arena collapse June 2023: https://globalnews.ca/video/9761158/railing-collapse-at-ufc-289-caught-on-video; https://www.youtube.com/watch?v=_tg0_23SgkI

El Alto University balustrade collapse:

https://en.wikipedia.org/wiki/Public_University_of_El_Alto

https://www.infobae.com/america/america-latina/2021/03/02/el-presidente-de-bolivia-lamento-la-tragedia-ocurrida-en-la-universidad-de-el-alto-y-aseguro-que-espera-el-pronto-esclarecimiento-de-los-hechos/

https://www.thenews.com.pk/print/798693-seven-students-plummet-to-death-at-bolivia-university

https://www.chicagotribune.com/espanol/sns-es-mueren-7-universitarios-al-caer-de-un-cuarto-piso-en-bolivia-20210302-6t2fwen3wjdifbczw7hyaaknde-story.html

https://metro.co.uk/2021/03/03/seven-students-dead-and-five-injured-after-university-railing-collapses-14182288/