STRUT AND TIE MODEL FOR DEEP BEAM DESIGN

A lthough the Strut and Tie
Method (STM) has been used
for several years in Europe1,2 and
has been included in the Canadian
Standard for the Design of Concrete
Structures3 since 1984 and the
AASHTO LRFD Bridge Specifications4
since 1994, it is a new concept
for many structural engineers in the
U.S. Procedures and recommendations
for the use of STM to design
reinforced concrete members were
discussed in a State-of-the-Art
Report from Joint ACI-ASCE Committee
445, Shear and Torsion,5 but
specific code requirements were not
incorporated into the ACI Building
Code until the 2002 edition,6 as
Appendix A. To help U.S. engineers
improve their ability to use STM for
analysis and design of concrete
members, Joint ACI-ASCE Committee
445 and ACI Committee 318-E,
Shear and Torsion, recently completed
a publication that contains a variety
of STM examples.7 The STM model
used here for the analysis and
design of a deep beam is not unique.
It should be noted that the STM
procedure in Appendix A of the ACI
Building Code (referred to as the
Code) is a strength limit-state design
approach. Serviceability limit-states
(for example, deflections and
reinforcement distribution) defined
in the main body of the Code must
also be checked.
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DESIGN of REINFORCED CONCRETE DEEP BEAMS Download File

An evaluation of pile cap design methods in accordance with the Canadian design standard

There are a number of design methods that have been described for the design of pile caps, but there has
been no consensus on which method provides the best approach for the working designer. This paper describes a study
conducted to establish the performance of several pile cap design methods, particularly with respect to the Canadian
standard, CSA A23.3-94. Previous research was examined to determine the basis of the design methods and the state
of current research. The design methods identified were then applied to pile caps for which test data were available.
The theoretical loads obtained using the various design methods were compared with the experimental loads. The results
of this study indicate that two design models of the five examined are the most suitable. This study also indicates
that the provisions of the Canadian design standard are adequate. A possible refinement of the strut-and-tie model incorporating
a geometric limit is also outlined.
Key words: building codes, footings, pile caps, reinforced concrete, structural design.
Résumé : Plusieurs méthodes de conception ont été décrites pour la conception des têtes de pieu, mais un consensus
n’a pas été atteint quant à savoir quelle méthode fournit la meilleure approche pour le concepteur. Cet article décrit
une étude effectuée pour déterminer le rendement de plusieurs méthodes de conception de semelles sur pieu, en particulier
par rapport au norme canadienne, CSA A23.3-94. Les recherches antérieures ont été examinées afin de déterminer
la base des méthodes de conception et l’état de la recherche actuelle. Les méthodes de conception identifiées ont
été appliquées aux semelles sur pieu pour lesquelles les données de tests étaient disponibles. Les charges théoriques
obtenues en utilisant les diverses méthodes de conception ont été comparées aux charges expérimentales. Les résultats
de cette étude indiquent que deux modèles de conception sur les cinq examinés étaient mieux adaptés. Cette étude indique
également que les dispositions de la norme canadienne de conception sont adéquates. Un raffinement possible du
modèle à treillis incorporant une limite géométrique est également souligné.
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PERENCANAAN STRUKTUR GEDUNG INSTALASI RAWAT INAP RSI SURAKARTA

Rumah Sakit Islam Surakarta adalah salah satu Rumah Sakit Islam
swasta yang berada dibawah naungan Yayasan Rumah Sakit Islam
Surakarta (YARSIS). RSI Surakarta beralamat di Jl. Ahmad Yani, Pabelan
Surakarta. RSI Surakarta memiliki berbagai fasilitas pelayanan yang
memadai baik pelayanan umum maupun khusus. Saat ini terdapat 5
gedung utama yang telah digunakan, 3 diantaranya adalah gedung yang
digunakan untuk instalasi rawat inap. Instalasi rawat inap tersebut terdiri
dari rawat inap untuk kelas Very Important Person (VIP), kelas I dan
keluarga miskin.
Rumah Sakit Islam Surakarta dalam perkembangannya masih
memerlukan ruangan untuk instalasi rawat inap khususnya kelas VIP
sehingga diperlukan penambahan jumlah instalasi rawat inap, maka dari
itu dilaksanakanlah pembangunan gedung rawat inap RSI Surakarta.
Dalam perencanaannya gedung ini dibuat 6 tingkat. Lantai 1 direncanakan
untuk ruang administrasi dan manajemen, lantai 2 untuk ruang rawat inap
kelas VIP, lantai 3,4,5 untuk ruang rawat inap kelas 1 dan lantai 6 untuk
ruang mesin.
Pembangunan instalasi rawat inap yang baru diharapkan mampu
meningkatkan pelayanan rumah sakit kepada pasiennya dan menjadikan
Rumah Sakit Islam Surakarta sebagai salah satu Rumah Sakit Islam yang
bonafid serta mengutamakan pelayanan. .Hal itulah yang melatar belakangi
dibangunnya gedung rawat inap ini.
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PERENCANAAN GEDUNG PERPUSTAKAAN 5 ( LIMA ) LANTAI DENGAN PRINSIP DAKTILITAS TINGKAT DUA

Perkembangan dunia ilmu pengetahuan ( science ) semakin cepat setiap
waktu dan akan terus berkembang sesuai dengan kemajuan jaman. Buku
merupakan sumber ilmu pengetahuan yang dapat membuat seseorang menjadi
mengerti akan ilmu pengetahuan, baik itu ilmu sosial maupun ilmu alam.
Memasyarakatkan budaya membaca dan memahami tentang ilmu pengetahuan
merupakan tujuan dari pendidikan nasional untuk meningkatkan Sumber Daya
Manusia ( SDM ) yang sudah lama digalakan oleh Pemerintah, untuk tujuan
tersebut dibutuhkan adanya prasarana penunjang. Prasarana penunjang tersebut
diantaranya adalah gedung perpustakaan.
Kodya Surakarta merupakan suatu kota yang cukup besar dengan
banyaknya penduduk yang membutuhkan suatu perpustakaan pusat kota yang
menyediakan buku-buku referensi untuk pengembangan SDM setiap anggota
masyarakat. Pembangunan perpustakaan pusat kota diharapkan akan dapat lebih
menggugah minat masyarakat kota untuk mempelajari ilmu pengetahuan sesuai
dengan minat dan bakat masing-masing.
Perencanaan gedung perpustakaan pusat kota perlu mempelajari struktur
organisasi suatu perpustakaan modern agar fungsi bangunan gedung tersebut
memenuhi syarat untuk pengembangan dimasa yang akan datang.
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PERENCANAAN STRUKTUR BETON BERTULANG UNTUK HOTEL TUJUH LANTAI (+1 BASEMENT) DENGAN PRINSIP DAKTALITAS PARSIAL DI DAERAH SUKOHARJO (TINJAUAN 2 DIMENSI

Sukoharjo merupakan kabupaten yang tengah berkembang di Propinsi
Jawa Tengah. Hal tersebut mengakibatkan meningkatnya bisnis dan perdagangan
di kabupaten Sukoharjo. Oleh karena itu banyak orang dari luar daerah yang
datang ke Sukoharjo untuk berbisnis maupun mengembangkan usaha yang
dimiliki. Diantara orang-orang tersebut tidak hanya melakukan kegiatannya
dalam sehari, mungkin untuk mengurus bisnisnya diperlukan waktu berhari-hari,
agar kegiatan yang dilakukan tersebut dapat berjalan dengan baik diperlukan
sarana yang memadai dan mendukung. Salah satu sarana yang dibutuhkan
adalah gedung perhotelan.
Gedung perhotelan adalah merupakan tempat untuk peristirahatan atau
penginapan setelah melakukan kegiatan perjalanan, namun dalam
perkembangannya hotel tidak hanya sebagai tempat peristirahatan atau
penginapan tetapi hotel juga dapat digunakan sebagai tempat pertemuan ataupun
rapat dengan rekan bisnis. Berkaitan dengan hal tersebut diatas maka penyusun
mencoba untuk merencanakan gedung perhotelan 7 lantai (+1 basement) di
Sukoharjo.
Salah satu faktor yang paling berpengaruh dalam perencanaan struktur
bangunan bertingkat tinggi adalah kekuatan struktur bangunan, dimana faktor ini
sangat terkait dengan keamanan dan ketahanan bangunan dalam menahan atau
menampung beban yang bekerja pada struktur. Indonesia termasuk negara rawan
dilanda gempa karena terletak dipertemuan Cirkum Pasifik dan Tran Asiatik.
Menurut SNI 03-1726-2002, Sukoharjo termasuk pada wilayah gempa 3 yaitu
merupakan daerah cukup besar kemungkinan terjadinya gempa maka untuk
itulah dalam perencanaan gedung bertingkat tinggi ini harus direncanakan dan
didesain dengan matang agar dapat digunakan sebaik-baiknya, nyaman dan aman
terhadap bahaya gempa bagi pemakai atau penguna struktur gedung.
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ANALISIS PENAMPANG KOLOM BETON BERTULANG PERSEGI BERLUBANG MENGGUNAKAN PCA COL

Pemasangan pipa pada kolom bangunan
(conduit) banyak ditemukan dalam struktur beton
bertulang. Pemasangan pipa ini dianggap
menguntungkan karena pipa di dalam kolom dapat
dimanfaatkan sebagai saluran listrik, air hujan, air
kotor, dan sebagainya sehingga bangunan akan
terlihat rapi tanpa pipa yang tampak dari luar.
Peraturan beton yang baru (SNI 03-2847-
2002) menyebutkan: Saluran pipa bersama kaitnya,
yang ditanam pada kolom tidak boleh menempati
lebih dari 4% luas penampang yang diperlukan untuk
kekuatan atau untuk perlindungan kebakaran.
Dari uraian di atas dapat disimpulakan
adanya permasalahan untuk memberikan saran-saran
mengenai pemakaian conduit di dalam penampang
kolom mengingat pentingnya elemen kolom dalam
menopang beban bangunan. Tujuan pembahasan
dalam artikel ini adalah mengetahui sejauh mana
pengaruh luas penampang lubang kolom yang
melebihi batas 4% terhadap luas penampang kolom
pada kemampuannya dalam memikul beban struktur
berdasarkan hasil diagram interaksi kolom.
Kekuatan kolom dalam memikul beban
didasarkan pada kemampuannya memikul kombinasi
beban axial (Pu) dan Momen (Mu) secara bersamaan.
Sehingga perencanaan kolom suatu struktur
bangunan didasarkan pada kekuatan dan kekakuan
penampang lintangnya terhadap aksi beban aksial dan
momen lentur. Untuk mempermudah mengetahui
kekuatan penampang kolom biasanya dibuat diagram
interaksi, yaitu suatu grafik daerah batas yang
menunjukkan ragam kombinasi beban aksial dan
momen yang dapat ditahan oleh kolom secara aman
(Wahyudi, 1997).
Pada Diagram Interaksi kolom (lihat Gambar
1), sumbu vertikal menunjukkan beban axial yang
dapat ditahan kolom sedang sumbu horizontal
menunjukkan beban momen yang dapat ditahan oleh
kolom.
Kolom yang mengalami beban axial murni
(Axial Load only) terjadi apabila kolom hanya
menahan beban sentris pada penampangnya (tanpa
eksentrisitas). Pada kondisi ini gaya luar akan ditahan
oleh penampang kolom yang secara matematis
dirumuskan dalam persamaan:
Pn = 0,8 x { 0,85. fc’. (Ag – Ast) + Ast.fy } (1)
dengan
fc’ = Kuat tekan beton yang disyaratkan
(MPa),
Ag = Luas penampang kolom,
Ast = Luas tulangan,
fy = Kuat tarik tulangan baja yang
diijinkan (MPa).
Apabila beban P bergeser dari sumbu kolom,
maka timbul eksentrisitas beban pada penampang
kolom, sehingga kolom harus memikul kombinasi
pembebanan aksial dan momen. Pada kolom yang
mengalami beban eksentris, apabila besarnya beban
aksial dan momen yang ditahan oleh kolom diplotkan
dalam gambar diagram interaksi kekuatan
penampang kolom, maka akan terdapat 4 jenis
kondisi keruntuhan penampang kolom.
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Pedoman Teknis Pelaksanaan Bangunan Infrastruktur

1. Pengertian Bangunan Infratstruktur
Bangunan Infrastruktur di suatu lingkungan diperlukan untuk mendukung aktivitas diluar
rumah.
Bangunan Infratstruktur adalah merupakan bangunan sarana dan prasarana pemukim pada
sebuah pemukiman untuk beraktivitas dan di luar rumah sekaligus pemenuhan sarana diluar
rumah.
2. Fungsi dan Manfaat Bangunan Infrastruktur
a Matigasi
Yakni merupakan akses penyelamatan umum termasuk evakuasi saat terjadi
bencana baik besar maupun kecil, termasuk seperti kejadian kebakaran bangunan
atau sampai dengan evakuasi orang sakit dan lain-lainnya.
b Akses Ekonomi
Yakni merupakan akses ekonomi umum termasuk akses mengangkut hasil panen
keluar ataupun masuk kedalam pemukimam, atau melewati kawasan untuk
menuju kawasan lainnya.
c Penjagaan Kebersihan Lingkungan
Pencegahan terhadap kekumuhan akibat sampah dengan cara mengumpulkan
kotoran atau sampah pada suatu tempat, sehingga mudah untuk diolah
d Stabilisasi tanah plengsengan
Memperkuat lapisan tanah terhadap pengaruh aliran banjir ataupun bahaya tanah
longsor.
e Pengaturan pembuangan air limbah
Pengumpulan air limbah usaha, rumah tinggal dan atau peturasan air hujan untuk
dikoleksi dan seterusnya dialirkan menuju saluran atau sungai yang terdekat agar
tidak menggenang dan mencegah berkembangnya penyakit.
f Dan lain-lain
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Analysis of Fiber Reinforced Polymer Composite Grid Reinforced Concrete Beams

In recent years, research on fiber-reinforced polymer (FRP)
composite grids has demonstrated that these products may be as
practical and cost-effective as reinforcements for concrete
structures.
1-5
FRP grid reinforcement offers several advantages
in comparison with conventional steel reinforcement and FRP
reinforcing bars. FRP grids are prefabricated, noncorrosive, and
lightweight systems suitable for assembly automation and ideal
for reducing field installation and maintenance costs. Research
on constructability issues and economics of FRP reinforcement
cages for concrete members has shown the potential of
these reinforcements to reduce life-cycle costs and significantly
increase construction site productivity.
6
Three-dimensional FRP composite grids provide a mechanical
anchorage within the concrete due to intersecting elements, and
thus no bond is necessary for proper load transfer. This type of
reinforcement provides integrated axial, flexural, and shear
reinforcement, and can also provide a concrete member with
the ability to fail in a pseudoductile manner. Continuing
research is being conducted to fully understand the behavior of
composite grid reinforced concrete to commercialize its use
and gain confidence in its design for widespread structural
applications. For instance, there is a need to predict the correct
failure mode of composite grid reinforced concrete beams
where there is significant flexural-shear cracking.
7 This type
of information is critical for the development of design
guidelines for FRP grid reinforced concrete members.
Current flexural design methods for FRP reinforced concrete
beams are analogous to the design of concrete beams using
conventional reinforcement.
8 The geometrical shape, ductility,
modulus of elasticity, and force transfer characteristics of FRP
composite grids, however, are likely to be different than
conventional steel or FRP bars. Therefore, the behavior of
concrete beams with this type of reinforcement needs to be
thoroughly investigated.
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JOURNAL OF THE CONSTRUCTION DIVISION

This paper summarizes results of a policy-level workshop attended by a distinguished
group of construction people representing owners, contractors, government, and educators. The
April f975 workshop was funded by the National Science Foundation and was sponsored by the
Construction Institute at Stanford University. In 2 full days of frank far-reaching deliberations,
these industry leaders attempted to define basic problems that the industry will face in the years
ahead.
In specific terms, the workshop was designed to: (1) Identify basic research needs in the
management of construction; and (2) define and formulate goals for basic research in this area.
The participants’ efforts were concentrated in four general subject areas, including: (l) Manpower
and organizational development; (2) management methodologies; (3) innovations in construction
methods; and (4) construction industry dynamics. Before outlining the results, however, this
paper will consider the nature of basic research and its relationship to construction.
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Experimental verification of a wireless sensing and control system for structural control using MR dampers

The performance aspects of a wireless ‘active’ sensor, including the reliability of the wireless communi-
cation channel for real-time data delivery and its application to feedback structural control, are explored
in this study. First, the control of magnetorheological (MR) dampers using wireless sensors is examined.
Second, the application of the MR-damper to actively control a half-scale three-storey steel building ex-
cited at its base by shaking table is studied using a wireless control system assembled from wireless active
sensors. With an MR damper installed on each floor (three dampers total), structural responses during
seismic excitation are measured by the system’s wireless active sensors and wirelessly communicated to
each other; upon receipt of response data, the wireless sensor interfaced to each MR damper calculates a
desired control action using an LQG controller implemented in the wireless sensor’s computational core.
In this system, the wireless active sensor is responsible for the reception of response data, determination
of optimal control forces, and the issuing of command signals to the MR damper. Various control solu-
tions are formulated in this study and embedded in the wireless control system including centralized and
decentralized control algorithms. Copyright 2007 John Wiley & Sons, Ltd.
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Reliability of Transfer Length Estimation from Strand End Slip

The force in a prestressing strand is transferred by bond to
the concrete in the release operation. At this stage, strand
stress varies from zero at the free end of the member to a
maximum value (effective stress). Transfer length is defined
as the distance required to develop the effective stress in the
prestressing strand.
1 Variation in strand stress along the
transfer length involves slip between the strand and the
concrete. The measurement of the strand end slip is an indirect
method to determine the transfer length.
2 Most experimental
standards 3-6
are based on this method, and it has been proposed
as a simple nondestructive assurance procedure by which the
quality of bond can be monitored within precasting plants.7
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Tensile Headed Anchors with Large Diameter and Deep Embedment in Concrete

Current anchorage designs for nuclear power plants in
Korea use large anchor bolts with diameters exceeding 2 in.
(50 mm), embedment depths exceeding 25 in. (635 mm), a
specified yield strength of 140 ksi (980 MPa), and a specified
ultimate strength of 155 ksi (1085 MPa). Whereas the tensile
behavior of smaller anchors has been studied extensively,
large anchors have not been adequately addressed. In the
research described herein, large anchors were tested in
tension to develop design criteria for anchors that are not
addressed by ACI 318-05, Appendix D,
1
or ACI 349-01,
Appendix B,
2 and to evaluate the applicability of
capacity-prediction methods developed for smaller anchors.
To evaluate the tensile behavior of anchors with large diameters
and embedment depths, various anchors, with diameters from
2.75 to 4.25 in. (69.9 to 108 mm) and embedment depths from
25 to 45 in. (635 to 1143 mm) were tested.
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Cyclic Load Behavior of Reinforced Concrete Beam Column Subassemblages of Modern Structures

The key to the design of ductile moment-resisting frames
is that the beam-to-column connections and columns must
remain essentially elastic throughout the load history to
ensure the lateral stability of the structure. If the connections
or columns exhibit stiffness and/or strength deterioration
with cycling, collapse due to P-Δ effects or to the formation
of a story mechanism may be unavoidable.
1,2
Four one-half scale beam-column subassemblages were
designed and constructed in turn, according to Eurocode 23
and Eurocode 8,
4
according to ACI 318-055
and ACI 352R-02,
6
and according to the new Greek Earthquake Resistant
Code7 and the new Greek Code for the Design of Reinforced
Concrete Structures.
8
The subassemblages were subjected to cyclic lateral load
histories so as to provide the equivalent of severe earthquake
damage. The results indicate that current design procedures
could sometimes result in severe damage to the joint, despite
the use of a weak girder-strong column design philosophy.
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Eccentric Reinforced Concrete Beam-Column Connections Subjected to Cyclic Loading in Principal Directions

Shear failure in beam-column connections, leading to the
collapse of reinforced concrete (RC) buildings, has been
observed in the post-earthquake reconnaissance.
1-3
The
cause of collapse has been attributed to the lack of joint
confinement, especially for the exterior and corner beam-
column connections without beams framing into all four sides.
Since the late 1960s, amounts of experimental investigations
on the seismic performance of RC beam-column connections
have been extensively studied. The majority of the exper-
imental programs have concentric beam-column connections
isolated from a lateral-force-resisting frame at the nearest
inflection points in the beams and columns framing into the
joint. Since 1976, Joint ACI-ASCE Committee 352 has
issued design recommendations for RC beam-column
joints.
4,5 Throughout the years, these guidelines evolved into
state-of-the-art reports
6,7
by integrating results of new
experimental programs. Finally, a number of these design
recommendations for beam-column connections have been
adopted in Chapter 21 of the ACI 318 Building Code8
for
seismic design. Current ACI design provisions are primarily
developed from test results of concentric beam-column
connections, whereas eccentric beam-column connections
are rather common in practice. Relatively few tests of eccentric
RC beam-column connections have been reported in the
literature to date.
9-19
To clarify the effect of eccentric beams
on the behavior of connections, Joint ACI-ASCE Committee
352 has called for additional research on this topic over the
past two decades,
5-7 and appointed a task group to review
and summarize previous research on eccentric RC beam-
column connections.
20
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Seismic Design Criteria for Slab Column Connections

Two-way slabs without beams are popular floor systems
because of their relatively simple formwork and the potential
for shorter story heights due to their shallow profile. This
structural system is common in regions of low to moderate
seismic risk, where it is allowed as a lateral-force-resisting
system (LFRS), as well as in regions of high seismic risk for
gravity systems where moment frames or shear walls are
provided as the main LFRS. Earthquakes, however, have
demonstrated that slab-column frames are not suitable as a main
LFRS in regions of high seismic risk because they are relatively
flexible and because of the potential for brittle punching shear
failures in the slab-column connection region.
In the last 40 years, a significant number of experiments
have been conducted to evaluate the performance of slab-
column connections under cyclic lateral loading. This infor-
mation has formed the basis of current code provisions and
guidelines for the design of slab-column connections under
combined gravity and lateral loading. As performance-based
seismic design (PBSD) becomes more common in structural
engineering practice, it is important to evaluate the
recommended limits for various structural systems with
respect to the latest experimental data and post-earthquake
observations. This paper focuses on the behavior and
design of interior slab-column connections under combined
gravity and lateral loading and serves to review current design
procedures, PBSD approaches, and relevant experimental data.
Equation (23), for drift capacity of these systems in terms of
the gravity shear ratio, is derived using the collected experi-
mental data. Finally, practical recommendations are provided
for the PBSD of slab-column connections.
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Simplified Punching Shear Design Method for Slab Column Connections Using Fuzzy Learning

INTRODUCTION
Flat plates consist of slabs directly supported on the
columns without beams. For this simple appearance, flat
plate systems have various economic and functional advantages
over other floor systems such as fast construction, low story
height, and irregular column layout. From a viewpoint of
structural mechanics, however, flat plates are structures of
complex behavior. Moreover, flat plates usually fail in a
brittle manner by punching at the slab-column connections
within the discontinuity region known as the D-region.
1,2
At
these connections, three-dimensional stresses are developed
due to the combined high shear and normal stresses creating
a stress state that is complex to analyze accurately.
3
For the last three decades, a significant amount of research
has been performed to investigate this complex problem of
concentric punching shear of reinforced concrete flat plates
by using various methods ranging from mechanical models
up to purely empirical models. In early models including
Yitzhaki
4 and Long and Rankin,
5 punching shear strength
was defined considering the flexural capacity of reinforced
concrete slabs. This was based on the experimental observation
that the punching shear strength was close to the flexural
capacities of the concrete slabs. Pralong6
and Nielsen7
derived lower bound and upper bound values for punching shear
strength based on the theory of plasticity. These formulations
did not consider the effect of flexural reinforcement on the
punching shear strength. Kinnunen and Nylander
8
developed
the first mechanical model for punching shear strength using
failure criteria based on the observation of shear cracks in the
experiments. In this model, the failure criteria were defined
by the inclined radial compressive stress and the tangential
compressive strain at the shear crack. Even though Kinnunen
and Nylander’s model
8
did not provide high accuracy in
punching shear strength predictions, it significantly contributed
to a better understanding of the failure mechanism of the
slab-column connections and enabled visualizing a rational
flow of forces in such connections. Alexander and
Simmonds
2
proposed a strut-and-tie model with concrete ties
to describe the load transfer in the slab-column connections.
Bažant and Cao9 developed a punching shear strength model
considering size effect of concrete based on principles of
fracture mechanics. The size-effect model was able to
explain the experimental observations of decreasing
punching failure shear stresses of slab-column connections
without reinforcement with increasing slab thickness.
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Flexural Behavior of Concrete Beams Strengthened with Near Surface Mounted CFRP Strips

In-service steel-reinforced concrete flexural members may
require strengthening due to material decay of the internal
reinforcement and surrounding concrete, errant design and
construction practice, increased service loads, and unforeseen
settlement and structural damage. These conditions require
structural retrofit to increase the flexural strength of the
section. A popular method of increasing the flexural strength
of beams, walls, and slabs is through external bonding of
fiber-reinforced polymer (FRP) plates and sheets. FRP materials
are characterized by high tensile strength and low unit
weight, and they are noncorrosive when exposed to chloride
environments. An excellent summary of research in this area
is available by Teng et al. (2002) and ACI has published a
design guide for strengthening concrete structures with
externally-bonded FRP materials (ACI Committee 440 2002).
Premature failure of externally-bonded FRP plates and
sheets can occur before the ultimate flexural capacity of the
strengthened section is achieved. This is typically due to
bond failure between the FRP and concrete or tensile peeling
of the cover concrete. Available research documenting this
behavior is abundant. Brena et al. (2003) reported debonding
of longitudinal carbon FRP (CFRP) sheets at deformation
levels less than half the deformation capacity of control
specimens. Nguyen et al. (2001) observed only a limited
increase in flexural capacity for beams strengthened with
partial length longitudinal CFRP sheets due to premature
delamination, or ripping, of the concrete cover surrounding
the steel reinforcement. For beams strengthened with CFRP
plate and fabric systems, Grace et al. (2002) identified brittle
failure by shear tension and debonding, respectively. Shin
and Lee (2003) reported failure of beams held under
sustained load and strengthened with CFRP laminates due
to rip-off type failure of the CFRP at loads well below the
ultimate
flexural capacity of the sections. Similar results have been
reported by Rahimi and Hutchinson (2001), Bencardino et al.
(2002), Arduini and Nanni (1997), Sharif et al. (1994),
Saadatmanesh (1994), and Mukhopadhyaya and Swamy
(1999). In addition to problems associated with bond failure,
external FRP plates are vulnerable to mechanical, thermal,
and environmental damage. It should be noted, however, that
mechanical anchors can be used to improve the peel resistance
of externally bonded FRP.
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Influence of Shear Reinforcement on Reinforced Concrete Continuous Deep Beams

Reinforced concrete deep beams are used in structures as
load distribution elements such as transfer girders, pile caps,
and foundation walls in tall buildings. Although these members
commonly have several supports, extensive experimental
investigations have brought simple deep beams into focus.
The behavior of continuous deep beams is significantly
different from that of simply supported deep beams. The
coexistence of high shear and high moment within the interior
shear span in continuous deep beams has a considerable
effect on the development of cracks, leading to a significant
reduction in the effective strength of the concrete strut,
which is the main load transfer element in deep beams.
1
Indeed, few experiments
1-3 were carried out on continuous
deep beams of shear span-to-overall depth ratio (a/h) greater
than 1.08. The results of simple deep beams tested by Tan et al.
4
and Smith and Vantsiotis,
5 however, showed that the relative
effectiveness of horizontal and vertical shear reinforcement
on controlling diagonal cracks and enhancing load capacity
reversed for deep beams having an a/h less than 1.0, that is,
horizontal shear reinforcement was more effective for an a/h
below 1.0, whereas vertical shear reinforcement was more
effective for an a/h lager than 1.0. Therefore, a reasonable
evaluation of the influence of shear reinforcement on
continuous deep beams having an a/h less than 1.0 requires
further investigation.
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Shake Table Studies of Bridge Columns with Double Interlocking Spirals

The current seismic design philosophy for reinforced
concrete structures relies on confinement of concrete to
provide the necessary ductility and energy dissipation
capacity of structural members. Confinement is mainly
provided by the transverse reinforcement, which in columns
usually consists of spirals in members with circular or square
shape and ties in those with square or rectangular cross
sections. Spirals confine concrete more effectively than
rectilinear ties because they counteract the dilation of
concrete through hoop action instead of a combination of
bending and hoop action that takes place in rectilinear ties.
As a result, to provide the same level of confinement, the
amount of tie reinforcement is greater than that provided by
spirals. Another advantage of spirals is that they are generally
easier to construct. The circular shape of spirals makes them
suitable for circular and square columns. To use the benefits
of spirals in rectangular columns, two or more sets of
interlocking spirals are used.
The Caltrans Bridge Design Specifications (BDS) and
Seismic Design Criteria (SDC)
2
are currently the only codes
in the U.S. that include provisions for the design of columns
with interlocking spirals. Because the amount of research on
interlocking spirals has been limited, the design provisions
are driven mainly by research on single spirals. Studies
3-5
were conducted on the effect of several design parameters,
including a comparison between interlocking spirals and
ties, horizontal distance between centers of the spirals,
quantity of transverse reinforcement, variation of the axial
load ratios, appropriate size and spacing of longitudinal bars
in the interlocking region, and cross section shape. These
studies generally concluded that flexural and shear
capacities of columns with interlocking spirals can be
conservatively estimated using current procedures. Conflicting
80% of the gross area (SDC).
2 A shear stress index was
defined as the average shear stress divided by 0.083√f ′
c
(MPa) (√f ′
c [psi]). This index represents the level of shear in
the column. In this study, two levels of shear were selected:
low index equal to 3 and high index equal to 7. These indexes
represent column shear stresses in real bridges. Actual
bridge columns are designed to be ductile and the load
capacity is controlled by flexure, although shear damage is
expected to increase as the shear index increases.
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Compression Field Modeling of Reinforced Concrete Subjected to Reversed Loading Formulation

The need for improved methods of analysis and modeling
of concrete subjected to reversed loading has been brought to
the fore by the seismic shear wall competition conducted by
the Nuclear Power Engineering Corporation of Japan.
1
The
results indicate that a method for predicting the peak strength
of structural walls is not well established. More important, in
the case of seismic analysis, was the apparent inability to
accurately predict structure ductility. Therefore, the state of
the art in analytical modeling of concrete subjected to general
loading conditions requires improvement if the seismic response
and ultimate strength of structures are to be evaluated with
sufficient confidence.
This paper presents a unified approach to constitutive
modeling of reinforced concrete that can be implemented
into finite element analysis procedures to provide accurate
simulations of concrete structures subjected to reversed
loading. Improved analysis and design can be achieved by
modeling the main features of the hysteresis behavior of
concrete and by addressing concrete in tension.
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