Structural design of floodways under extreme flood loading

Abstract

Purpose Current methods for floodway design are predominately based on hydrological and hydraulic design principles. The purpose of this paper is to investigate a finite element methods approach for the inclusion of a simplified structural design method into floodway design procedures. Design/methodology/approach This research uses a three-dimensional finite element method to investigate numerically the different parameters, geometric configurations and loading combinations which cause floodway vulnerability during extreme flood events. The worst-case loading scenario is then used as the basis for design from which several structural design charts are deduced. These charts enable design bending moments and shear forces to be extracted and the cross-sectional area of steel and concrete to be designed in accordance with the relevant design codes for strength, serviceability and durability. Findings It was discovered that the analysed floodway structure is most vulnerable when impacted by a 4-tonne boulder, a 900 mm cut-off wall depth and with no downstream rock protection. Design charts were created, forming a simplified structural design process to strengthen the current hydraulic design approach provided in current floodway design guidelines. This developed procedure is demonstrated through application with an example floodway structural design. Originality/value The deduced structural design process will ensure floodway structures have adequate structural resilience, aiding in reduced maintenance and periods of unserviceability in the wake of extreme flood events.

Qualitative investigations into floodways under extreme flood loading

“…F I G U R E 2 Survey question: In your experience what is the likelihood that a floodway, inclusive of protection, will sustain damage during extreme flood events? (Greene et al, 2020b).…”

“…F I G U R E 5 Survey question: Which soil type have you found floodway failure to be most common in? (Greene et al, 2020b).…”

“…This F I G U R E 6 Survey question: During extreme flood events, have you found increased sediment load, such as organic debris (logs) and boulders from landslides, bank erosion and other processes, contributed to floodway failure as a result of being conveyed by floodwaters and impacting the floodway structure? (Greene et al, 2020b).…”

“…Impact loading in a floodway structure occurs when the floodway is submerged, and debris, such as floating logs or rolling boulders impact the superstructure. Greene et al (2020b) undertook a comprehensive Australian-based industry survey in 2020 to investigate the experiences of asset owners concerning extreme flood events and the prevalence of impact-related failures, thus providing a qualitative dataset in relation to practical experiences post extreme flood events. In the international context, two other floodway specific surveys were undertaken by Lohnes et al (2001) and Gautam and Bhattarai (2018).…”

“…Research conducted by Lokuge et al (2019) identified common structural attributes relating to vulnerable floodways and summarized the limitations of using finite element analysis to design floodways. Greene et al (2020a) utilized finite element analysis to extensively investigate floodways and reported that the worst‐case loading scenario, using load combinations documented in AS5100.2:2017, Bridge Design – Design loads was impact loading. Impact loading can be considered as an accidental loading, like an earthquake, which a resilient structure shall withstand as an ultimate limit state loading.…”