A preliminary study on shear capacity of historical reinforced concrete beams

Abstract

In European cities there are many reinforced concrete (RC) constructions belonging to the early 20th century and, in most cases, these pieces of work so rich in historical, architectural and cultural significance urgently require maintenance and restoration.Reinforced concrete works, from the origins until the release of the first technical standards, were built by applying patented systems (e.g. Monnier's, Hennebique's) that were often the result of individual intuitions more than scientific and technical knowledge. This is one of the reasons that many of the structures built in those years, and still surviving, could not be considered reliable with regard to the structural safety, as it is presently intended.In this scenario, the evaluation of RC beam shear capacity becomes crucial. In this article, analysing the tests carried out in Stuttgart in the early 20th century, a preliminary study on the shear capacity assessment of historical RC beams is presented. The aim is to verify the applicability to these kinds of beams of the relations given for new constructions in the present codes. Moreover a novel formulation for the transversal shear capacity for historical RC beams with U-shaped plates is proposed. Keywords: Load Path Method, reinforced concrete, shear capacity, Strut-and-Tie Model INTRODUCTIONThe main task to be faced in the restoration of the early RC constructions is the assessment of their actual structural capacity, in order to provide the proper guidelines for retrofitting, rehabilitation and conservation.It is not so straightforward to apply to ancient concrete structures the same methods of analysis that are used for the design of new constructions, and this is particularly true with regard to shear capacity. In fact, models and formulations used in the standard design practice are mainly based on the experimental observation of the behaviour of real-scale structural elements that are different from those of the early RC constructions. The constructive technique and the structural details concerning the shear reinforcement have changed much in the last century, much more than those regarding longitudinal reinforcement.Present methods to evaluate shear capacity seem to be not applicable to old RC structures mainly due to the following reasons:

Anchorage of Reinforcement Bars in Hennebique R.C. Structures

“…The intrinsic weaknesses of the early reinforced concrete structures, among which the Hennebique system plays the major role, is well known and addressed by several authors [4,[17][18][19][20][21][22]. The two main issues need specific attention: i) concrete compressive strength, affecting the bending capacity of the beams; ii) shear capacity, which depends on the amount of shear reinforcement and on the efficiency of its anchorage.…”

“…Brencich, M. Nebiacolombo 2 Nowadays warehouses, industrial facilities, a large number of bridges and buildings, either residential and public, built according to the Hennebique system, are in service. For many of them retrofitting is needed due to several reasons, such as material degradation, re-functioning and, mainly for strategic buildings such as schools, hospitals and public offices, for their seismic upgrade.The intrinsic weaknesses of the early reinforced concrete structures, among which the Hennebique system plays the major role, is well known and addressed by several authors [4,[17][18][19][20][21][22]. The two main issues need specific attention: i) concrete compressive strength, affecting the bending capacity of the beams; ii) shear capacity, which depends on the amount of shear reinforcement and on the efficiency of its anchorage.This paper addresses a specific problem: the anchorage performance of either bending and shear reinforcing bars.…”