CONCEPTUAL DESIGN OF BOWSTRING BRIDGES WITH STRESS RIBBON TIE

In this paper the conceptual design of tied-arch bridges is examined. A proposal for a particular kind of bowstring bridges, with an upper deck and a stress ribbon footbridge placed between the arch footings is discussed. The double structure allows to avoid horizontal forces into foundations when functional requirements lead to differentiate pedestrian and road traffic. After a general discussion about classical tied-arches, the main parameters involved in the design of the proposed solution are discussed and a case-study is presented

IL METODO DEGLI SCHEMI ELASTICI PARZIALI NELLA COSTRUZIONE A SBALZO DEI PONTI AD ARCO

In questo lavoro viene presentato uno studio sulle sequenze di tesatura degli stralli nei ponti ad arco costruiti per sbalzi successivi con l’ausilio di tiranti provvisori. In particolare viene presentato il metodo degli schemi elastici parziali, proposto per la determinazione degli sforzi iniziali nei cavi. Tale metodologia è stata dapprima applicata sui ponti strallati e viene estesa in questo studio al caso dei ponti ad arco costruiti per sbalzi successivi. La trattazione teorica è seguita da un’applicazione numerica su un caso studio di un ponte ad arco in calcestruzzo

CREEP EFFECTS AND STRESS ADJUSTMENTS IN CABLE-STAYED BRIDGES WITH CONCRETE DECK

In construction stages of cable-stayed bridges with prestressed concrete deck, the influence of creep on stresses and strains is very important in order to foresee the final patterns of internal forces and displacements. In cantilever construction, the concrete deck can be considered, in each stage, as a continuous beam resting on elastic restraints, which modify with successive additions of new segments, until the last one has been assembled. In these stages stress relaxation in concrete occurs as well as vertical displacements increase. Ehen structure has been closed by inserting midspan segment, stress redistribution begins, due to creep. Deformation and internal force development in construction and service life modify stay stresses such as deck and pylon final profiles. It is necessary to prevent undesirable deformed shape of deck and pylon and to control the final stress pattern of deck and stays. The requested final geometry of the bridge is reached by adjusting stay axial forces during construction. A study is presented in which, by taking into account creep effects, the optimization in terms of deck and pylon deformed shape can be achieved through a sequence of stay force adjustments during construction stages. The presented analysis is based on the theory of aging linear viscoelasticity in order to give a useful tool for the conceptual design of cable-stayed bridges with concrete deck. The proposed procedure allows engineers to design by reducing and avoiding creep effects instead of calculating them with refined models since the first design step

Monitoring of stress distribution in damaged small-scale masonry walls by using two innovative sensors

Structural Health Monitoring (SHM) represents a strategic solution for the preservation of cultural heritage buildings. Existing masonry structures often suffer reductions in mechanical performances due to physiological aging of material constituents, external actions, and effect of catastrophic natural events. In many cases, the prompt prediction of damage in masonry elements is difficult and it can cause sudden collapses, compromising the safety of people. The proposed experimental study examines the effectiveness of two low-cost and innovative stress sensors, i.e. piezoelectric and capacitive stress sensors, for SHM of masonry structures. To this scope, the sensors were embedded in the mortar joints of two small-scale clay brick and calcarenite masonry wall specimens consisting of three panels. Experimental tests were carried out by applying a constant vertical compressive load at the top of each specimen and simulating the damage with a progressive reduction of the cross-section of one of the panels. During the tests, the vertical stress distributions (and their variations), were monitored by the sensors. Experimental outcomes from sensor reading were then compared to that numerically provided by a refined finite element simulation of the test. Results will show that vertical stress variations in masonry structures can be effectively accounted by the adopted sensors and potentially interpreted for the early prediction of structural damage