In today’s market, it is imperative to be knowledgeable and have an edge over the competition. ACI members have it…they are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them.
Read more about membership
Become an ACI Member
Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
ACI World Headquarters
38800 Country Club Dr.
Farmington Hills, MI
ACI Middle East Regional Office
Second Floor, Office #207
The Offices 2 Building, One Central
Dubai World Trade Center Complex
Phone: +971.4.516.3208 & 3209
Chat with Us Online Now
Feedback via Email
Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 248 Abstracts search results
October 1, 2020
Yao, Y.; Bakhshi, M.; Nasri, V.; Mobasher, B.
Precast concrete segments are the predominant support method used in tunnels dug by Tunnel
Boring Machines (TBM) in soft ground and weak fractured rock, providing the initial and final ground
support. Conventionally, steel bars are used in concrete segments to resist tensile stresses due to all
loading cases from the time of casting through service condition. With traditional reinforcement, a
significant amount of time and labor are needed to assemble the cages and place the reinforcing bars.
Fiber reinforced concrete (FRC) has become more attractive for its use in tunnel lining construction as
a result of improved post-cracking performance, crack control characteristics and capability of partial
replacement of steel bars. Due to the strength requirements in large-diameter tunnels, which are
subjected to embedment loads and TBM thrust jack forces, the use of FRC is not adequate as the sole
reinforcing mechanism. Therefore, the hybrid fiber-reinforced concrete (HRC) combining both rebars
and steel fibers is frequently used in practice. Tunnel segmental linings are designed for load cases
that occur during manufacturing, transportation, installation, and service conditions. With the
exception of two load cases of TBM thrust jack forces and longitudinal joint bursting load, segments
are subjected to combined axial force and bending moment. Therefore, P-M interaction diagrams have
been used as the main design tool for tunnel engineers.
Standard FRC constitutive laws recently allow for a significant residual strength in tension zone
below the neutral axis. However, design capacity of HRC segment is significantly underestimated
using conventional Whitney’s rectangular stress block method, especially for tension-controlled
failure, since the contribution of fibers in tension zone is ignored. Methods that currently incorporate
contribution of fibers on P-M diagrams are based on numerical and finite-element analyses, which are
normally more complicated and not readily to be implemented for practical design tools. Closed-form
solutions of full-range P-M interaction diagram considering both rebar and fiber contributions are
presented in this paper for HRC segments. The proposed model is verified with experimental data of
compression tests with eccentricity as well as other numerical models for various cases of HRC
sections. Results show that using appropriate material models for fiber and reinforcing bar, engineers
can use the proposed methodology to obtain P-M interaction diagrams for HRC tunnel segments.
Plückelmann, S.; Breitenbücher, R.
In special cases, concrete members are exposed to high locally concentrated loadings. Such
concentrated loadings lead to a multi-dimensional stress state beneath the loaded area. Due to
the load diffusion, large splitting tensile stresses are generated in the upper regions of the
concrete member (i.e. St. Venant disturbance zone) and spread along directions perpendicular
to the load. In order to resist these splitting tensile stresses, the state of the art is to reinforce
concrete members with transverse steel reinforcement. An alternative approach is to add steel
fibers to the concrete matrix. However, regarding economic concerns it may not appropriate
to reinforce the entire concrete member with an adequate high amount of steel fibers, rather
only those zones where high splitting stresses are expected.
The main objective of the presented experimental study was to investigate the load-bearing
and fracture behavior of hybrid concrete elements with splitting fiber reinforcement under
concentrated load. For this purpose, in a first step, hybrid specimens were produced
containing both plain and fiber concretes. The reference specimens consisted exclusively of
plain concrete, while the hybrid specimens were partially strengthened with various types of
steel fibers only in the St. Venant disturbance zone, instead of a full range fiber
reinforcement. The thickness of the reinforcement layer was varied in order to determine the
optimal configuration of fiber reinforcement. Taking into account the influence of the casting
direction on the fiber orientation and consequently on the bearing and fracture behavior, the
hybrid specimens were cast either in standing or in lying molds by means of a “wet-on-wet”
casting technique. These hybrid elements were then tested under concentrated load.
The test results showed that under concentric loads the maximum bearing capacity of the
hybrid specimens increased progressively with growing thickness of the fiber reinforced
concrete layer. In contrast to the plain concrete specimens, the fiber reinforcement led to a
remarkable improvement in the post-cracking ductility. Compared to the fully reinforced
specimens, the hybrid specimens that were only reinforced in the St. Venant disturbance zone
exhibited - besides an almost identical bearing capacity - a similar local behavior in the postcracking
zone. Furthermore, a significant impact of the casting direction on the bearing as
well as fracture behavior could be proved.
Barros, J.A.O.; Foster, S.J.
For the development of reliable physical-mechanical models for predicting the behaviour
of fibre reinforced concrete structures at service and strength limit conditions, constitutive
models simulating comprehensibly the governing phenomena must be used. In this context,
simulating the post-cracking mechanisms of the fibres, and their symbiotic relationship with
the cementitious matrix that surrounds them, is required for the development of realistic
modelling approaches that accurately represent empirical observations. Several experimental
test setups and inverse analysis procedures have been proposed to derive the fundamental
stress-crack width ( –w) law, but a consensus still does not exists on the best strategy for its
determination. In structures governed by shear, fibre reinforcement increases the stiffness and
shear stress transfer across a crack, but a methodology to capture the contribution of fibres in
this regards is challenging. To overcome this, a clear strategy is needed in deriving
relationships that simulate fibre reinforcement mechanisms in the mobilized fracture modes
and, also, develop design approaches capable of capturing the relevant contributions of the
fibres. This study firstly reviews current inverse analysis models used to describe the tensile
(Model I fracture) relationship for FRC and, secondly, discusses a newly proposed model,
referred to as the integrated shear model (ISM). The ISM is developed from mesoscale
observations from gamma- and X-ray imaging on FRC elements under Modes I and II
fracture conditions. The resulting model is compared to test data reported in the literature and
a good correlation is observed.
Galeote, E.; Blanco, A.; Cavalaro, S.H.P.; de la Fuente, A.
The influence of size effect becomes an issue particularly relevant during the
characterization stage of concrete at laboratory scale. The dimensions of the specimens have a
direct influence on the strength measured and, therefore, selecting an appropriate specimen
size is of utmost importance in order to obtain representative results to be used in the design
of a structure. The notched beam test to characterize FRC is among the most extended
methods to determine the design parameters of the residual strength, mainly associated to
crack openings of 0.5 mm and 2.5 mm (fR1 and fR3, respectively). The main objective of this
study was to determine the influence of the beam dimensions on these two parameters. For
this, an analytical model able to reproduce the flexural behavior of FRC was developed.
Additionally, an experimental program involving high performance fibre reinforced concrete
(HPFRC) beams of dimensions 40x40x160, 100x100x400 and 150x150x600 mm was
conducted. The parameters of the analytical model were calibrated for each specimen
dimension using the results of the experimental program. The results show a clear influence
of the size of the specimen, mainly attributed to the area of fracture and the crack crosssection.
March 1, 2020
John S. Ma
The U.S. Nuclear Regulatory Commission (NRC) defines seismic Category 1 structures as the structures (buildings) that should be designed and built to withstand the maximum potential earthquake stresses for the particular region where a nuclear plant is sited. Seismic Category 1 structures have been designed for ground-shaking intensity associated with a safe-shutdown earthquake (SSE) – the intensity of the ground motion that will trigger the process of automatic shutdown of the reactor in operation. The SSE generates floor response spectra at different floor elevations in a building, and these spectra and their associated forces are used for the design of piping and piping anchors and equipment and equipment anchors at their floor locations. The NRC policy requires that the seismic Category 1
structures whose collapse could cause early or/and large release of radioactive materials into the atmosphere to be
analyzed/designed for “no collapse” during the ground-shaking intensity of a review-level earthquake (RLE), which
is 1.67 times that of an SSE. Most seismic Category 1 concrete structures, such as containment and shield buildings
(curved cylindrical wall; see Figs. 1 and 2 in the next section) and containment internal structures (straight wall; see
Fig. 1), use walls to resist earthquakes.
This paper presents guidelines for the performance-based seismic design for these wall-typed structures that could
meet the NRC policy. The method consists of (1) proportioning wall thickness based on shear stress of 6√fc’ (0.5√fc’ megapascals (MPa)) generated by SSE ground motions, (2) limiting vertical compressive stress in walls to less than
0.35 fc’, (3) providing minimum percentage of reinforcement of 1.0 percent to prevent steel reinforcing bar fracture,
(4) subjecting the building design to nonlinear dynamic response analyses under RLE ground motions, (5) identifying
any members and their connections in the building that have failed or collapsed during the RLE ground motions,
(6) increasing reinforcement or wall thickness, or both, to provide additional strength or/and ductility for the failed or
collapsed members and their connections, and (7) resubjecting the revised building design to the nonlinear dynamic
response analyses as stated in step (4) until no collapse of the building and its members and their connections. This
performance-based seismic design method is a direct, transparent, and scientific answer to whether these important
seismic Category 1 structures meet the NRC’s policy that they will not collapse during the RLE ground motions.
Examples of using the nonlinear dynamic response analyses are cited and described. Guidelines for the performance-based
seismic design of seismic Category 1 concrete Structures are listed at the end of this paper.
Results Per Page
Please enter this 5 digit unlock code on the web page.