1,721,075 research outputs found
Numerical analysis of the effects of PBO-FRCM confinement on RC columns
No full textThis paper presents a finite element (FE) analysis on the
behavior of reinforced concrete (RC) squared and
rectangular columns strengthened by PBO-FRCM, under
axial force and bending moment. The modeling technique
adopted for the compressive behavior of confined
concrete is previously validated developing FE models for
specimens of plain concrete wrapped by PBO-FRCM and
comparing the numerical results with those obtained by
experimental tests on squared and rectangular confined
columns. Then, the model of the RC element is developed
reproducing the load condition of columns in a MRF
loaded by horizontal forces with constant axial load
applied to the pillar during the analysis. The numerical
model is validated against experimental results obtained
by the authors in a previous study
Experimental Behaviour of the Friction Dissipative Device for Hybrid Steel Trussed Concrete Beam to Column Joint
No full textConnessioni trave-colonna dissipative per attrito sono sempre pi ̆ frequentemente impiegate per la realizzazione di strutture antisismiche resilienti grazie alla loro facilit‡ di progettazione, affidabilit‡ di comportamento, ridotta perdita di prestazioni nel tempo e
influenza del comportamento dalle condizioni ambientali, nonchÈ elevate prestazioni garantite da grande rigidezza, facilit‡ di regolazione della resistenza della connessione, elevata e stabile capacit‡ dissipativa e ridotta complessit‡ costruttiva. Qui vengono riportati i risultati dei test condotti su dispositivi di attrito lineare, che Ë il componente principale della connessione dissipativa, e su un
prototipo in scala reale di una connessione fra trave reticolare in acciaio ibrida in calcestruzzo (HSTCB)-colonna recentemente proposta. Per analizzare in modo approfondito la funzionalit‡ del dispositivo di attrito proposto in termini di dissipazione di energia, Ë
stato testato sotto cinque carichi ciclici con diverse ampiezze. I risultati hanno dimostrato l'efficacia delle soluzioni tecniche adottate
per la progettazione del dispositivoFriction dissipative beam-to-column connections are rising popularity to design resilient earthquake-resistant structure due to their ease of design, reliability of behavior, reduced loss of performance over time and influence of environmental conditions on the behavior. High performance is guaranteed by high initial stiffness, ease of tunning connection strength, high and stable dissipative capacity, and reduced construction complexity are further appreciated features. The research is focused on test results conducted on linear friction devices, which is the main component of the dissipative connection, and on a full-scale prototype of a recently proposed friction-based hybrid steel trussed concrete beams (HSTCBs)-to-column connection for moment resisting frame. In order to deeply analyze the functionality of proposed friction device in term of energy dissipation, it has been tested under five cyclic loadings with different amplitudes. The results proved the efficiency of the technical solutions adopted for the device design
Advances on the Use of Geopolymer Recycled Aggregate Concrete in Construction
No full textGeopolymer cement is made up of waste materials, an efficient alternative
to ordinary cement in order to reduce the emission of carbon dioxide. The
use of geopolymer recycled aggregate concrete (GRAC) in structural elements has
been an object of recent several experimental research in which the behaviour of
either the material or structural element was investigated. A review paper will be
done critically to compile the present research on the use of GRAC in construction.
It will cover the effect of different materials composition in GRAC and the
factors affecting its strength focusing on recycled aggregate’s replacement ratio.
The problems related to the strength of GRAC structural members, their tensile
and flexural behaviour will also be addressed. It will also help in finding the future
prospects of the use of GRAC in construction
RC beams retrofitted by FRP oriented in any direction: Influence of the effectiveness factors
Full text linkShear strength of FRP-retrofitted RC beams is usually influenced by different brittle failure modes characterizing
the collapse of the FRP reinforcement. The most significant analytical models for assessing the shear strength of
FRP-retrofitted RC beams reflect the effect of brittle failure through an effectiveness factor “R”, which reduces
the ultimate tensile strength of FRP. The brittle collapse of FRP reinforcement often leads to a lower shear
contribution by steel stirrups due to hindering of the yielding of all stirrups involved by critical cracking. Some
analytical models consider this phenomenon introducing a further effectiveness factor “r”, which reduces the
yielding strength of stirrups. The key differences characterizing many of the shear models are represented by the
expressions used for assessment of the effectiveness factors. This paper focuses on the influence of effectiveness
factor models in analytical predictions provided by different shear models. The reduction of the shear contribution of steel stirrups due to FRP brittle failure is modeled as dependent on the FRP wrapping scheme, through
the ratio between FRP effective strain and steel yielding strain. To highlight the influence of the effectiveness
factor for steel stirrups, two analyses are performed through different shear models, considering the effectiveness
factor for FRP only, and considering the effectiveness factor for both FRP reinforcement and steel stirrups. The
results are discussed considering two databases, one constituted by beams whose FRP reinforcement and steel
stirrups are arranged at right angles to the beam axis, and one in which the FRP is arranged at angles different
from 90◦
The structural behaviour of hybrid steel-trussed concrete beams: A literature review of experimental tests and theoretical models
Full text linkHybrid Steel-Trussed Concrete Beams (HSTCBs), introduced in civil construction around the 70s, combine a steel truss within an in-situ cast concrete core, often with a steel or concrete bottom plate. Initially favoured in industrial buildings for their semi-prefabricated construction and ability to span large distances with contained depths, HSTCBs have subsequently attracted scientific interest in residential construction, focusing on static and seismic response. The technical literature on this topic highlights that HSTCBs do not follow the same mechanical rules of RC or steel-concrete composite beams, necessitating specific insights into their behaviour under flexure, shear, and seismic conditions. This review aims to collect the major scientific results obtained in the last twenty-five years by several researchers in Italy and abroad, beside the outcomes of some relevant earlier studies. The reviewed papers encompass findings from experimental campaigns on weldings, push-out test specimens, simply supported beams and beam-to-column joints. Some of these studies also incorporate proposals for analytical formulations aimed at offering design-oriented and code-compliant prediction models, alongside finite element simulations to replicate the strengthening mechanisms. Following a thorough synthesis of the primary findings to date, the literature review underscores notable gaps in knowledge and still open issues, particularly concerning long-term performance and size-effect laws
Stress transfer mechanism investigation in hybrid steel trussed-concrete beams by push-out tests
No full textResults of push-out tests carried out on Hybrid Steel Trussed–Concrete Beams (HSTCBs) before and after the concrete
casting are presented and interpreted. Firstly, in order to check the ability ofweldings before casting, tensile
tests were performed on specimens reproducing different types of welded joints. Simplified design formulae
were used to predict their ultimate strength. Secondly, results obtained by push-out tests on specimen representative
of the beambefore and after the concrete casting are presented and discussed. Finally, simplified analytical
models proposed by the current European building codewere adapted to the specific typology to roughly predict
the ultimate strength obtained by push-out tests on specimens complete with concrete casting
Experimental Investigation of the Shear Response of Precast Steel-Concrete Trussed Beams
No full textThe results of an experimental campaign of three-point bending tests on precast composite beams, named hybrid steel-trussed concrete beams (HSTCBs), are provided. HSTCBs are typically constituted by a precast steel truss embedded in a block of concrete cast in place. Two series of specimens were manufactured, designed such that shear failure would occur, and tested under positive and negative bending moment. The experimental results obtained showed that fragile shear failure occurred in almost all cases, evidencing the crisis of the compressed concrete strut involved in the collapse mechanism. Yielding of the steel members provided ductility to the system, especially in those cases in which the mechanical properties of the concrete were adequate and allowed the failure of the strut to be delayed. Some of the more accredited expressions for prediction of shear resistance available in the literature were used to assess the shear capacity and compared against those experimentally obtained for all specimens. The existing formulas mainly refer to classical reinforced concrete (RC) beams, but analytical models recently developed for HSTCBs were considered for interpreting the test results. On the basis of the experimental outcomes and the results obtained from their analytical interpretation, comments and design considerations on the main parameters ruling the resisting mechanism occurring in the tested beam typology are provided
CYCLIC BEHAVIOR OF AN INNOVATIVE FRICTION DEVICE FOR RC COLUMN-HSTCB CONNECTION
No full textSeismic events result in the loss of human lives due to the collapse of structures. Engineers are trying to figure out an efficient way to ensure dissipative behavior of structures with the primary objective to protect human lives and as secondary to minimize economic loss and to ensure the swift return of users. Beam to column joints play a significant role in the overall seismic performance of structures. For precast concrete and steel moment resisting frames (MRFs) various solutions have been proposed for beam-to-column connections while fewer have been proposed for cast-in-situ reinforced concrete (RC) structures. In this paper, the experimental behavior of a friction-based beam-to-column connection (BCC) for moment resisting frame having hybrid steel trussed concrete beams (HSTCBs) is investigated. In order to mitigate the reduction of strength, stiffness and effect of shear force acting on beam to column joint, the BCC is equipped with a friction device. Thermal-sprayed aluminum was used as a friction material on steel angles based on its high friction coefficient (0.6), and satisfactory performance confirmed by the experimental approach. The specimen tested was constituted by a beam-column joint equipped with a friction device with T-stub on the top chord and central plate on the beam side and steel angles on the column side, a 1.55 m long Hybrid Steel Trussed Concrete Beam (HSTCB), and a 3.3m long column. The connection between the different components was established by bolts. In order to simulate the effect of dead load an axial load of 500kN was applied to the column. Displacement-controlled tests were carried out by applying on the beam at a distance of l= 1.31m from the center of rotation and displacement history defined according to ACI 374.2R-13 (2013). In total, 5 tests were performed with three amplitudes of maximum displacement of ± 21.5 mm, ± 38 mm, ± 71 mm. From the forcedisplacement curves, the initial results showed that the beam-to-column joint provides full stable hysteresis loops, and no damage or cracking was observed on the tested specimen. The test confirmed the ability of disc springs in limiting the loss of bolt preload. An interesting phenomenon was observed in some test, due the inclusion of new bolts. A sudden variation of bolt preload at the start cycles was detected, since friction surface and bolts need to adjust by themselves at the start of the cyclic load. Bolt preload remains constant in the subsequent cycles. It was also observed that the applied sliding force in not symmetric as expected, namely in the case of the hogging (positive) moment, there is a lower sliding force while in the case of the sagging (negative) moment there is higher sliding force of about 15/20% at entire sliding branch of ± 71mm. This is due to two phenomena as with increase in contact pressure due to bugging of plates and due to the variation of lever arm of the external force, due to large displacement effect related to the test setup. As the applied displacement increases there is found a reduction of the lever arm which increases the external force able to activate the sliding of the devices
Seismic response of RC frames with steel-concrete truss beams equipped with beam-to-column and column-to-foundation friction damper connections
Full text linkFriction Damper Devices (FDDs) at the Beam-to-Column Connections (BCCs) are a suitable solution to prevent
losses of performance due to cracking and bond losses caused by the high percentage of reinforcement that characterize the panel
zone of Moment Resistant Frames with Hybrid Steel Trussed-Concrete Beams (HSTCBs). Here it will be shown that excellent seismic
performance can be obtained only when FDDs at the BCCs are used in conjunction with self-centering dissipative connections
at the column bases. To this aim, comparison of the seismic performance of traditional and innovative RC structures built using
HSTCBs is performed, focusing on the different level of damage experienced by RC beams, columns and panel node zones belonging
to traditional and innovative frame
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