Proposal for New Design Provisions for Impactive and Impulsive Loading in ACI349 and ACI359/ASME Section III Division 2

Abstract of the technical paper presented at:
SMiRT 26
Berlin, Germany, August 8–13, 2021

Prepared by: Nebojsa Orbovic¹, Adeola Adediran², Ola Jovall^3
1Canadian Nuclear Safety Commission
²Bechtel, USA
³SCANSCOT, Sweden

Abstract

The Joint Task Group, made up of members of the ACI 349 Committee for Concrete Nuclear Structures, the ACI 359/ASME Section III Division 2 Joint Committee for Concrete Containments for Nuclear Reactors and the ACI 370 Committee for Blast and Impact Load Effects, put in place an activity to propose new design provisions for impactive and impulsive loadings for nuclear safety-related structures. A single document, ACI 349R4 (draft), was developed to cover both ACI 349 (2013) and ACI 359/ASME Section III Division 2 (2019) design needs, with a consistent design methodology and acceptance criteria. The major change introduced in the proposal is a shift from ductility factors to support rotations for global, flexural behaviour under impulsive loading. Moreover, the acceptance criteria define the structural performance and the level of damage associated with support rotations. Four levels of damage are defined: superficial, low, medium and severe. The level of damage is associated with the safety function attributed to the civil structures: protection of safety-related structures, systems and components (SSCs) or leak tightness. Based on this document, ACI 349 and ACI 359 will adopt applicable portions and structural acceptance criteria according to the safety requirements.

The acceptance criteria covers design-basis as well as design-extension accidents and events. Structural acceptance criteria are already defined in terms of support rotations for conventional structures in Unified Facilities Criteria document UFC 3-340-02 (2008). However, it was recognized even in the current version of the standards (e.g. ACI 349, Appendix F) that one acceptance criterion is not enough to precisely define non linear behaviour of structural elements. In comparison to conventional structures, it is necessary to have an additional criterion. In the current code, this criterion is the rotational capacity of the reinforced concrete section. This criterion is replaced by strain limits in concrete and in reinforcement, as the strain criteria can be easily correlated to the damage level and be easily implemented in the design software using input from Finite Element (FE) models. Modern national safety requirements (Canadian Nuclear Safety Commission, REGDOC-2.5.2, 2014) and international guidance (International Atomic Energy Agency, Safety Reports Series No. 87, 2017) for nuclear power plants already implement this type of structural acceptance criteria.

In terms of impactive loading, empirical equations are provided for local behaviour with their domain of validity. The empirical equations are provided for scabbing and just perforation. The local behaviour is correlated to the global, flexural behaviour in order to provide a consistent design for the loading cases with combined impactive and impulsive loading (e.g. aircraft crash).

Conclusions

A proposal for consistent design provisions for safety-related nuclear concrete structures and nuclear containment was developed in a single document, ACI 349R4 (draft), under Joint Task Group ACI 349/359/370. The design criteria addresses both design-basis and design-extension accidents including events and provides a consistent set of criteria for both global and local behaviour in terms of support rotations; strain criteria for global behaviour; as well as empirical equations, with their validity domain for local behaviour.

References

ACI 349R4 (draft), Report on the Design for Impactive and Impulsive Loads for Nuclear Safety Related Structures.
ACI 349 (2013), Code Requirements for Nuclear Safety-Related Concrete Structures.
ASME BPVC Section III Division 2 (2019), Code for Concrete Containments.
Canadian Nuclear Safety Commission (2014), REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants.
International Atomic Energy Agency (2017), Safety Reports Series No. 87, Safety Aspects of Nuclear Power Plants in Human Induced External Events: Assessment of Structures.
Unified Facilities Criteria UFC 3-340-02 (2008), Structures to Resist the Effects of Accidental Explosions.

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