Tuesday, November 19, 2013

Project #tweetprop: Shear capacity at the continuous support

The fourth proposition of my dissertation is the following:

The shear capacity of reinforced concrete members near to continuous supports is at least equal to the shear capacity near to simple supports, contrarily to the recommendations of NEN6720:1995

or in Dutch:

De dwarskrachtcapaciteit van gewapend betonnen elementen nabij doorgaande opleggingen is minstens gelijk aan de capaciteit nabij vrije opleggingen, in tegenstelling tot het NEN 6720:1995 voorschrift

The old Dutch Code (NEN 6720:1995 [1]) prescribes an increase in capacity for loads close to the support, but only if their are placed near to a simple support (or end support). This effect was expressed through the factor kλ, which was applied as an enhancement factor on the shear capacity.

In Eurocode 2 (NEN-EN 1992-1-1:2005 [2]), the effect of direct load transfer is taken into account by reducing the contribution to the shear stress at the support for loads close to the support. The code does not make a difference between simple and continuous supports anymore.

In our experiments, we tested with the concentrated load close to the simple support and close to the continuous support. These experiments taught us that the capacity at the continuous support is often larger than at the simple support, and that it is by all means safe to say that the capacity at the continuous support is at least equal to the capacity at the simple support. You can find the entire parameter analysis for the influence of the moment distribution at the support in §4.5 of my dissertation.

The experimental analysis shows that the shear capacity at the continuous support is at least equal to the shear capacity at the simple support. As such, the recommendations from the old Dutch code do not correspond to our experimental results.

[1] Normcommissie 351001, 1995, "NEN 6720 Technische Grondslagen voor Bouwvoorschriften, Voorschriften Beton TGB 1990 – Constructieve Eisen en Rekenmethoden (VBC 1995)," Civieltechnisch centrum uitvoering research en regelgeving, Nederlands Normalisatie-instituut, ; Delft, The Netherlands, 245 pp.

[2] CEN, 2005, "Eurocode 2: Design of Concrete Structures - Part 1-1 General Rules and Rules for Buildings. NEN-EN 1992-1-1:2005," Comité Européen de Normalisation, Brussels, Belgium, 229 pp.

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