90 | INTERPRAEVENT 2016 – Extended Abstracts
INTRODUCTION
Vulnerability of buildings is relevant for flood risk management and, more specifically, for the design of local structural protection measures. Focusing on inundation mapping of flood hazard processes and the determination of impacting forces on buildings, current methods in practice are based on simplify- ing assumptions and quantitative-empirical knowl- edge rather than physical-based approaches (Maz- zorana et al., 2014). Material intrusion processes are not considered, as well as any interactions of the building structure with the adjacent flow field.
The work presented within this paper addresses on these issues. Within a case study analysis, building perfusion processes were analyzed by use of a 3d-hydrodynamic numerical model. With a specific focus on the characteristics of torrential hazards and thereby also considering the influence of sediments, material intrusion processes and the spatially distributed determination of forces acting on the building envelope are experimentally analyzed.
3D-NUMERICAL MODELLING OF BUILDING PERFUSION AND INTERACTIONS WITH FLOODING
Solely considering clear water conditions and checking for capabilities and limits of numerically simulating the building-fluid-interaction, a section of the Rio Vallarsa in the village of Laives (South Tyrol, Italy) was chosen as case study area (Hofer, 2014). The river drains a catchment area of 27.5 km² and has mainly a fluviatile process char- acter. Within the simulations roughly 150 m of the rigid channel in the settlement area of Laives and the adjacent flood plain were covered.
In accordance to the Department of Hydraulic Engineering (Autonomous Province of Bolzano), flooding is expected in this area at discharges higher than the HQ30-value. One specific building, situated orografically right (Figure 1, middle), is
considered in detail within the simulations: (i) flooding of the building and (ii) impacting fluid forces on the structure were analyzed.
The 3d-numerical simulations were carried out with the FLOW-3D software. Both, steady state simulations with discharges in the range
80-120 m³/s and design flood hydrographs were executed. Concerning impacting forces and the influence of the building perfusion processes on the flow pattern in the flood plain, three modelling options for the building were compared: (a) the current state situation including basement and ground floor level with all inner walls and doors and windows set to be fully open, (b) a fully blocked building structure as it is typically assumed within extensive 2d-flood plain modelling and (c) the current state situation of the building as in (a) but including a set of permanent measures for object protection (Hofer, 2014).
Figure 1 (center) illustrates the extent of the numerical model (FAVOR-model in FLOW-3D) and the building structure (left). Further, results from the steady state simulation with a discharge of 104 m³/s and building type (a) are shown (right).
The presented hydraulic case study application indicates that building perfusion processes have a rather limited influence on the adjacent flow field.
This holds specifically for steady-state simulations as illustrated in Figure 1, right, as the retention effect of the building has a minor impact on the process of flooding there. However, the simulations allow for a spatially and temporarily distributed determination of impacting forces on both, inner and exterior walls. Critical components for flooding and the effects of object protection measures can be pointed out (Hofer, 2014).
Mutual influences of flood hazard processes and
buildings – basic research issues within numerical and experimental modelling
Bernhard Gems, Dr.1; Bruno Mazzorana, Dr.2; Thomas Hofer3; Sven Fuchs, PD Dr.4; Michael Sturm1; Markus Aufleger, Prof. Dr.1
DATA ACQUISITION AND MODELLING (MONITORING, PROCESSES, TECHNOLOGIES, MODELS)
IP_2016_EA284
INTERPRAEVENT 2016 – Extended Abstracts | 91
RESEARCH ON IMPACTING FORCES ON BUILDINGS AND MATERIAL INTRUSION PROCESSES
The determination of expected losses at buildings due to torrential hazards and its relation with reconstruction costs is generally based on empirical functions (Totschnig and Fuchs, 2013). Straightfor- ward relations of process intensities and the extent of losses, gathered by the analysis of historic flood events and the information of object-specific restoration values, are used. In this case, vulnera- bility analysis of buildings is based on a purely physics-based concept, considering also process intrusion into elements at risk. Damage-relevant, morphodynamic processes are modelled within a physical scale model test (1:30). Thereby, specific focus is on the analysis of flood discharges with a rather high fraction of sediments. The experimental analysis is firstly done by analyzing the impacts on vertical and skewed plates, including also openings for material intrusion. Further, the impacts on specific buildings within the test site, the fan apex of the Schnannerbach torrent (Tyrol), are analyzed.
The buildings are reconstructed within the physical scale model, including basement and first floor and all relevant openings on the building envelopes.
The tests are based on a detailed analysis of the hazard processes on the alluvial cone of the Schnannerbach torrent (Gems et al., 2014).
The research is currently in progress at the Univer-
sity of Innsbruck and accomplished within the project “P 27400-NBL” funded by the Austrian Science Fund FWF. Modelling results and findings mean a significant expansion of the present meth- ods for vulnerability and flood risk assessment. For practical application, they may provide extensive information to support during hazard zone map- ping and management and as well during the planning phase of local technical protection meas- ures.
REFERENCES
- Gems B., Sturm M., Vogl A., Weber C., Aufleger M. (2014). Analysis of damage causing hazard processes on a torrent fan - scale model tests of the Schnannerbach Torrent channel and its entry to the receiving water. Digital Proceedings of the Inter- praevent 2014 in the Pacific Rim, Nara, Japan.
- Hofer T. (2014). 3D-numerische Modellierung der Durch- und Umströmung von Infrastrukturobjek- ten (Gebäuden). Master Thesis, University of Innsbruck (in German).
- Mazzorana B., Simoni S., Scherer C., Gems B., Fuchs S., Keiler M. (2014). A physical approach on flood risk vulnerability of buildings. Hydrol Earth Syst Sci 18, 3817-3836.
- Totschnig R., Fuchs S. (2013). Mountain torrents:
quantifying vulnerability and assessing uncertain- ties. Eng. Geol. 155, 31-44.
Figure 1. Considered building structure (left); FAVOR model (FLOW-3D) (center); results from the steady-state simulation with the discharge Q = 104 m³/s after 140 s of simulation (right)
KEYWORDS
flood risk management; vulnerability; material intrusion; numerical modelling; physical scale model
1 Unit of Hydraulic Engineering, University of Innsbruck, AUSTRIA, bernhard.gems@uibk.ac.at 2 Autonomous Province of Bolzano, Department of Hydraulic Engineering, ITALY
3 MWV Bauingenieure AG, Baden, SWITZERLAND
4 Institute of Mountain Risk Engineering, University of Natural Resources and Life Sciences, Vienna, AUSTRIA
