1,721,012 research outputs found
Method to design fiber-reinforced elastomeric isolators (U-FREIs) and application
No full textThis paper proposes a method to design unbounded fiber-reinforced elastomeric isolators (U-FREIs) which, on the basis of the building mass, loads and target isolation period, allows the designer to determine the isolator geometrical dimensions and stiffness characteristics. Many studies in the literature demonstrate that U-FREIs are a viable alternative to Steel Reinforced Elastomeric Isolators (SREIs), making it feasible to employ seismic isolation in residential buildings, even in developing countries. However, currently there are only few references in the literature which give precise directions on how to design U-FREIs to take account of their peculiarities and differences with respect to SREIs. The method proposed herein imposes the fulfillment of three conditions, which take account of U-FREIs peculiar behavior. A step by step procedure developed for square shaped isolators is provided as guide to the application of the proposed design method. A case study is presented, both utilizing the proposed U-FREIs and equivalent SREIs. The differences in the performance of the building, obtained with the two different devices, are discussed
Stability Assessment of the Brick Masonry Veneer Walls of an Existing Reinforced Concrete Building
No full textThis paper presents a stability assessment of the masonry veneer walls of a recent building, which displayed visible damage in its masonry cladding system. The investigation campaign, conducted on-site, provided valuable data about the structural performance of the veneer walls. The assessment of out-of-plane stability was carried out analytically, in accordance with the Italian Building Code and the recommendations of UNI EN 1996-1-1:2022, which guide the design and analysis of masonry structures. The effects of thermal variations on the veneer walls stability are also assessed. From the results of the investigations and subsequent analyses, the paper identifies the primary causes of the observed damages. To address these issues and ensure compliance with the safety requirements prescribed by the Code, a series of safety interventions are proposed
On the modeling of anchored bars in tensioned concrete: exponential and linear formulations of the local bond law
No full textSeismic Behavior of Exterior Beam-Column Connections with Plain Bars and Effects of Upgrade
No full textCyclic load tests on six reinforced concrete (RC) exterior beamcolumn
subassemblages simulating joints of buildings constructed
before the 1970s, with nonoptimal reinforcing details to resist
earthquakes, are described. The exterior beam-column joints were
reinforced by plain bars and lacked transverse reinforcement, and
the longitudinal beam bars were poorly anchored. Two of them had
inadequate beam top reinforcement. All of the beam-column joints
were also tested after the upgrade, except one, which was upgraded
and then tested for the first time. The proposed upgrade techniques
were aimed at providing an effectual anchoring to the beam longitudinal
bars and at increasing strength and stiffness of the beamcolumn
joints. As expected, the performance of reference specimens
(without upgrade) was found to be unsatisfactory in terms of lateral
load capacity and stiffness. The improvement in the performance of
the upgraded specimens is demonstrated
Sliding Instability of Fiber-reinforced Elastomeric Isolators in Unbonded Applications
No full textFiber-reinforced isolators not anchored to the structure represent a new development in seismic isolation.
Their light weight, low cost and great ease of installation, in comparison with conventional elastomeric
isolators, could allow to extend the use of these valuable devices to seismic protection of housing
and commercial buildings, particularly in developing countries. As demonstrated in studies available in
the literature, fiber-reinforced isolators match the behavior of steel-reinforced ones. However the friction
behavior between such new devices and the structure has not been investigated yet. This paper describes
an experimental study on elastomeric isolators reinforced by bi-directional carbon fiber fabrics performed
to investigate the static friction at contact surfaces. The isolators were placed in contact with concrete
surfaces and subjected contemporaneously to compressive stress and shear strains. Friction
behavior was analyzed in terms of isolator sliding with respect to the concrete sub- and super-structure.
Influence on friction behavior of different parameters, such as level of compressive stress, rubber typology,
concrete roughness, aging and loading rate, was investigated. The tests showed that, in relation to
the value of the applied compressive stress, uncontrolled sliding of the isolator can occur by increasing
the shear force. This unstable condition is called sliding instability herein. The experimental results are
explained and the limit values of the compressive stress needed to avoid sliding instability is provided
both for new and aged isolators, under quasi-static loading conditions. It is demonstrated that quasistatic
tests are reasonably conservative with regard to safety. Patterns of stresses and relative displacements
based on the experimental results are also proposed
A Simple Method for Evaluating the Maximum Slip of Anchorages
No full textThe analytical solutions to the bond problem
for monotonically increasing loads are developed
for a monomial exponential local bond stress-slip relationship
(law) – “exact solution” –, a linear local law –
“proposed solution” – and a constant bond stress distribution,
such as that recommended by the Eurocode.
The three solutions are thoroughly developed for the
pull-out of a bar embedded in a cylindrical element,
with longitudinal concrete in tension. For short anchorages,
which undergo a rigid motion and whose “exact
solution” requires a complex iterative procedure, the
“proposed solution” explicitly provides very accurate
bond stress distributions. On the basis of this accuracy,
an approximate expression for the slip distribution
is derived. The proposed approximate solution is
the first one providing a direct slip expression for short
anchorages. Approximate explicit expressions for the
maximum bond stress and the maximum slip are also
given. The comparison between the maximum slip values
measured during experimental tests and the corresponding
values obtained from the proposed approximate
expression demonstrates the accuracy of the latter
Seismic retrofitting of a reinforced concrete building with strongly different stiffness in the main directions
No full textThe displacement capacity of the existing reinforced concrete building under study does not satisfy the seismic Italian Code requirements. The modal analysis highlights that the structure has strongly different stiffnesses along its main directions and, in the stiffer one, translation is coupled with torsion. To improve the seismic behavior of the building, it is proposed to install an external steel frame with stiff braces along the side of the structure which is the most deformable due to torsional effect. Conversely, in the orthogonal direction, where the ductility demand is much higher, external steel frames with dissipative braces are used. The effectiveness of the proposed solution is checked by push-over analysis
Tensile Tests for the Improvement of Adhesion between Rubber and Steel Layers in Elastomeric Isolators
Full text linkSteel reinforced elastomeric isolators are currently the most used bearings for seismic
isolation purposes. The steel reinforcements are cut to the desired shape, sandblasted, cleaned with
acid, and coated with bonding compound during the manufacturing process. Then the elastomer
and steel layers are stacked in a mold and subjected to vulcanization so that they are glued together
and constitute a single body. Good adhesion between the layers is very important for the correct
functioning of the device. Adhesion conditions become critical when the isolators are subjected to
tensile stresses, which arise under direct tensile actions or large shear strains. To analyze the
influence of changes in the manufacturing process on the isolator adhesive behavior, the authors
performed tensile tests on square‐shaped small‐scale specimens rather than expensive shear tests
on full‐scale isolators. Hence, the adhesion behavior between elastomer and steel layers was
investigated through the tensile tests discussed herein. Among the influencing parameters that were
considered, it was found that an increase in vulcanization time does not improve the adhesion, but
it may actually worsen the capacity of the isolator in terms of strength. Moreover, it was found that
using elastomer without an oily component improves the adhesion between the layers and increases
the isolator’s dissipative capacity
LONG-TERM STRUCTURAL DEFICIENCIES IN A MAT FOUNDATION ON CLAY SOIL
No full textA 3-story building with a mat foundation consisting of a slab on a grid of grade beams performed poorly on clay soil. Cracking of the slab became rogressively worse as a result of the incorrect esign and fluctuations in the groundwater pressure under the foundation. The cyclic presence and absence of water rusted the steel reinforcement, and the sulfates in the clay soil caused formation of ettringite in the concrete. Plastic hinges formed in the slab and settlements occurred, causing damage to the beams. The situation is still in progress and may lead to the collapse of the structure under normal service conditions. The geotechnical and structural investigations performed to survey and assess the aforementioned problems are described in this paper. The causes and the consequences of the detected anomalies are analyzed, and a prediction of potential future structural problems is provided. A strengthening procedure is proposed, and an estimate of the cost to realize it is provided. Recommendations are offered to help avoid the problem in new constructions
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