Hou 2016
Hou 2016
Hou 2016
Engineering Structures
journal homepage: www.elsevier.com/locate/engstruct
a r t i c l e i n f o a b s t r a c t
Article history: This paper focuses on a new type of steel-concrete composite beams consisting of cast-in-place concrete
Received 10 September 2015 slabs on Precast Prestressed Concrete Decks (PPCDs). To evaluate flexural performance of such composite
Revised 14 July 2016 beams, this research team conducted an experimental investigation on twelve specimens. Test results
Accepted 31 July 2016
show that the composite beams with PPCDs can exhibit desirable and stable flexural performance under
monotonic loading. Based upon the test results, this paper also evaluates the influence of some key design
parameters (e.g., concrete slab thickness, amount of shear studs and longitudinal reinforcement ratio) on
Keywords:
flexural performance of the composite beams.
Testing
Precast
2016 Elsevier Ltd. All rights reserved.
Flexure
Composite
Beam
1. Introduction but will reduce headroom and more importantly result in extra
costs.
Steel-concrete composite beams combine the advantages of This research team explored a practical solution to the above
structural steel such as high strength, ductility and ease of erection issue, in which the Precast Prestressed Concrete Decks (PPCDs)
and those of reinforced concrete such as high rigidity and low cost. were used as an alternative to the steel corrugated decks of con-
A conventional steel-concrete composite beam consists of a steel ventional steel-concrete composite beams. The PPCDs, which will
beam with I-shaped cross-section supporting a concrete slab cast be described in detail in a following section, are a new type of con-
on a steel corrugated deck. Through application of appropriate con- struction units recently developed for modular construction [8].
nectors (e.g., headed shear studs) between the steel beam and the While keeping the other favorable features of conventional com-
concrete slab, their relative slip can be restrained, enabling shear posite beams, the composite beams with PPCDs offer additional
force transfer between them and achievement of the composite aesthetic values (such as flat surface and similar or even reduced
beam action [1]. Recent investigations, both analytical and experi- floor depth) and can be more affordable in some cases.
mental, have shown that this type of structural components can The objective of this research was to evaluate flexural perfor-
exhibit high stiffness and strength, and behave in a ductile manner, mance of the composite beams with PPCDs. Through testing of a
making them a viable and cost-effective alternative to traditional series of twelve specimens, this research team investigated dam-
structural steel or reinforced concrete beams [27]. Nevertheless, age progression, failure mechanism and other aspects of the com-
there are remaining issues limiting the widespread acceptance of posite beams under monotonic loading. The test results obtained
such composite beams. For example, the wrinkled surface of steel from this investigation form a basis for a better understanding of
corrugated deck as part of the steel-concrete composite beam the fundamental behavior of such composite beams and help pro-
may be unfavorable to building owners and architects in some mote their applications in future building constructions. The fol-
cases. Adoption of suspended ceilings could alleviate this problem, lowing sections describe in detail the proposed composite beams,
specimen design and construction, material properties, test setup,
loading program, observations, test results, and influences of key
construction parameters on flexural performance of the composite
Corresponding author at: Dept. of Civil and Environmental Engineering, beams.
California Polytechnic State University, San Luis Obispo, CA 93407, USA.
E-mail address: bqu@calpoly.edu (B. Qu).
http://dx.doi.org/10.1016/j.engstruct.2016.07.065
0141-0296/ 2016 Elsevier Ltd. All rights reserved.
406 H. Hou et al. / Engineering Structures 126 (2016) 405416
Fig. 1. A typical PPCD (before removal of extended rebars and bottom concrete panel at the PPCD ends).
H. Hou et al. / Engineering Structures 126 (2016) 405416 407
(a) cross-section (b) side view (extended rebars and bottom panel
at the ends may be cut out if needed)
(d) Section A-A of CB1 to CB10 (e) Section A-A of CB11 (f) Section A-A of CB12
Table 1
Summary of specimen details.
Specimen Rib orientationa Amount of PPCDs hf (mm) a (mm) s (mm) na/nr Longitudinal rebars q (%)
number diameter (mm)
CB1 Perpendicular 6 130 40 130 1.0 12 8 0.29
CB2 Perpendicular 6 140 40 130 1.0 12 8 0.27
CB3 Perpendicular 6 150 40 130 1.0 12 8 0.25
CB4 Perpendicular 6 130 0 130 1.0 12 8 0.29
CB5 Perpendicular 6 130 20 130 1.0 12 8 0.29
CB6 Perpendicular 6 130 60 130 1.0 12 8 0.29
CB7 Perpendicular 6 130 40 100 1.30 12 8 0.29
CB8 Perpendicular 6 130 40 150 0.87 12 8 0.29
CB9 Perpendicular 6 130 40 130 1.0 12 10 0.46
CB10 Perpendicular 6 130 40 130 1.0 12 12 0.65
CB11 Parallel 2 130 40 130 1.0 12 8 0.29
CB12 b b 130 b 130 1.0 12 8 0.29
a
Relative to beam longitudinal direction.
b
Not applicable.
Specimens CB1, CB4, CB5 and CB6, which were included to address concrete modulus of elasticity experimentally obtained from the
the influence of overlap width, were tested at the early stage of the prisms (150 mm 150 mm 300 mm) according to the Standard
investigation. Overlap width of the other specimens was deter- for Test Method of Mechanical Properties on Ordinary Concrete [13].
0
mined based upon test data of these specimens. Table 2 presents the values of f c:cube , fc,cube, fc,prism and Ec for the
Construction of each specimen with PPCDs followed the prac- cast-in-place concrete and the concrete used in the precast panels,
tice of conventional steel-concrete composite beams with steel respectively.
corrugated decks. First, the shear studs were welded to the steel The steel rebars with nominal diameters of 8 mm, 10 mm and
beam; then the PPCDs were installed as the formwork; next, the 12 mm were HRB400. The steel wires with the nominal diameter
joints between adjacent PPCDs were filled with M20 mortar (see of 4.8 mm were Grade 1570. Flanges and webs of the steel beams
Fig. 4) and the rebars were placed according to design (see both used Q345 steel; however, their strength values were slightly
Fig. 5); last, the concrete slab was cast and cured. different. Table 3 presents the yield strength, fy, ultimate strength,
fu, and modulus of elasticity, Es of each type of steel.
4. Material properties
5. Test setup loading scheme and instrumentation
Mix of the M20 mortar was designed according to the Specifica-
tion for Mix Proportion Design of Masonry Mortar (JGJ/T98-2010) Four-point bending tests were performed for all the specimens.
[11]. However, actual strength of the M20 mortar was not experi- Fig. 6 schematically shows the test setup. As shown, each specimen
mentally measured. According to the design, the masses of Grade was simply supported at the ends and two identical point loads
42.5 cement, lime and sand (with the water content of 3% and were applied at its one-third points. At each loading step, Zones
the dry density of 1450 kg/m3) in each cubic meter of the M20 1 and 3 of the beam (see Fig. 6) were subjected to constant shear
mortar are 292.5 kg, 57.5 kg and 1500 kg, respectively. Nominal demands while Zone 2 was subjected to pure bending.
yield and ultimate strengths of the steel in shear studs are Prior to testing, the ultimate flexural resistance, Mua, of each
240 MPa and 400 MPa, respectively. However, these properties specimen was calculated through a stress diagram assuming that
were not experimentally verified. Grade 52.5 cement, natural sand the entire steel beam section yields due to tension and the stress
with the fineness modulus of 2.88 (fine aggregate), crushed stones over the compression zone of the slab section is uniform [14]. Load
with the nominal maximum size of 20 mm (coarse aggregate), was monotonically increased through force control during each
water, and fly ash were used in concrete. The masses of cement, test. The load increment, which is one tenth of the load causing
fine aggregate, coarse aggregate, water and fly ash in each cubic Mua in the specimen, was added at each loading step. The target
meter of the cast-in-place concrete are 312.4 kg, 686.7 kg, load of each step lasted ten minutes and fifteen minutes before
1196.1 kg, 159.7 kg and 55.2 kg, respectively, while the masses of and after occurrence of the first visible crack in each specimen.
the corresponding mixtures in the precast concrete are 402.9 kg, The loading protocol was continued beyond the load associated
575.7 kg, 1205 kg, 155.2 kg and 71.2 kg, respectively. with Mua and concluded when one of the following scenarios
Properties of concrete, steel rebars, steel wires, and steel beam occurred: (1) significant visible sliding was observed between steel
flange and beam web were determined from tests of material beam and concrete slab; (2) concrete severely crushed; and (3)
samples. For concrete, tests were conducted on both cubes specimen stability requirements were no longer seemed to meet.
(100 mm 100 mm 100 mm) and prisms (150 mm 150 mm Each specimen was instrumented to record the following
300 mm). Given that concrete strength associated with the response quantities of interest: strains in concrete slab and steel
150 mm 150 mm 150 mm cubes is more commonly used. beam, deflections at the midpoint and two loading points of each
The concrete strength obtained from the 100 mm 100 mm composite beam; and the slip between steel beam and concrete
100 mm cubes was converted to that associated with the slab at the ends of each specimen.
150 mm 150 mm 150 mm cubes based upon the prior recom-
mendations (i.e., modifying the concrete strength associated with
Table 2
100 mm 100 mm 100 mm cubes by the coefficient of 0.95) Properties of concrete (unit: MPa).
[12]. The compressive strengths associated with the 100 mm
0
Category f c:cube fc,cube fc,prism Ec
100 mm 100 mm cubes, 150 mm 150 mm 150 mm cubes,
0 3.51 104
and 150 mm 150 mm 300 mm prisms are denoted as, f c:cube , PPCD 56 53.2 34.05
Cast-in-place concrete 40.6 38.6 25.82 3.23 104
fc,cube and fc,prism, respectively. In addition, Ec represents the
H. Hou et al. / Engineering Structures 126 (2016) 405416 409
Table 4
Summary of critical bending moments and beam deflections.
Specimen Mcr (kN m) My (kN m) Mu (kN m) My/Mu Py (kN) dy (mm) Py/dy (kN/mm) du (mm) du/dy
CB1 112.5 135.5 247.1 0.55 301.1 7.58 39.72 41.83 5.52
CB2 121.5 142.3 251.1 0.57 316.2 11.48 27.55 52.39 4.56
CB3 139.5 152.1 258.8 0.59 338.0 8.79 38.45 38.26 4.35
CB4 135.0 147.3 254.7 0.58 327.3 8.74 37.45 50.41 5.77
CB5 121.5 136.3 237.6 0.57 302.9 7.75 39.08 45.17 5.83
CB6 135.0 142.6 242.1 0.59 316.9 10.63 29.81 39.58 3.72
CB7 135.0 153.6 262.8 0.58 341.3 9.32 36.62 56.30 6.04
CB8 103.5 128.3 216.0 0.59 285.1 9.56 29.82 36.17 3.78
CB9 112.5 139.7 261.0 0.54 310.4 7.37 42.12 39.49 5.36
CB10 135.0 151.2 252.0 0.60 336.0 7.48 44.92 36.92 4.94
CB11 135.0 123.5 255.6 0.48 274.4 10.65 25.77 48.05 4.51
CB12 112.5 146.3 257.0 0.57 325.1 7.71 42.17 76.56 9.93
partially due to the better integrity of the full-depth cast-in-place close-to-ultimate load levels, Specimen CB7 retains the approxi-
concrete slab in Specimen CB12 in comparison with Specimen mately linear strain distribution, suggesting that plane section
CB1. The higher neutral axis location and higher slab compressive remained primarily plane in the specimen. However, the strain
strain in Specimen CB12 are consistent with the fact that Specimen profiles of Specimen CB8 cease to follow the linear distribution at
CB12 achieved a higher flexural resistance in comparison with the corresponding load levels. This is because the shear stud inter-
Specimen CB1 (see Table 4). val in Specimen CB8 is larger (see Table 1), resulting higher slip
Fig. 12(a) and (b) presents the strain profiles under different deformations between the concrete slab and steel girder at higher
loading levels recorded at the mid-span locations of Specimens load levels (which will be discussed in detail in the following sec-
CB7 and CB8, respectively. Fig. 12(c) and (d) shows the progres- tion). Although the neutral axis location is higher in Specimen CB8
sively developed strain profiles across the concrete slabs of the compared with CB7 at the comparable close-to-ultimate states, the
two specimens recorded at one load application point. Note that less successful development of the composite action due to the slip
Specimens CB7 and CB8 had identical design parameters (see between the concrete slab and steel girder led to the lower flexural
Table 1) except that Specimen CB7 had a smaller shear stud strength in Specimen CB8 (see Table 4).
interval compared with Specimen CB8. As shown, at relatively The yield strain of beam flange is also included in Figs. 11 and
low load levels, both specimens have linear strain profiles. At the 12. As shown, fibers at the top portion of the steel beam are not
412 H. Hou et al. / Engineering Structures 126 (2016) 405416
(a) strain profiles across the entire beam section (b) strain profiles across the entire beam section
(at midpoint of CB1) (at midpoint of CB12)
(c) strain profiles across the concrete slab (d) strain profiles across the concrete slab
(at one loading point of CB1) (at one loading point of CB12)
yielded at the close-to-ultimate states. Table 5 compares the neu- result trend are observed among all specimens. All the curves tend
tral axis location, Zur (defined as the distance from the neutral axis to exhibit increased slopes under a higher mid-span bending
to the interface between steel girder and concrete slab) of each moment, suggesting that the slip increases to a higher degree
specimen under the close-to-ultimate moment, Mur. Moreover, as when a composite beam is loaded into inelastic range. At the end
shown in Figs. 11(a) and (b) and 12(a) and (b), the tensile strain of the test, the beam end slip was found to be less than 0.1% of
recorded at the bottom of the concrete slab is higher than that of beam span (i.e., 2.7 mm) in all specimens.
the top of the steel beam at a given loading level, suggesting that
slip deformations occurred at the interface of concrete slab and
7. Discussion of influences of key parameters
steel beam. Table 6 further reports the strain at the top of concrete
slab, ect, and that at the bottom face of bottom flange of steel beam,
As listed in Table 1, some design parameters were intentionally
esb, in Zone 2 of each specimen under the critical bending moments
varied in the specimens. As such, the test data allow a further dis-
including Mcr, My and Mur.
cussion on the influences of these parameters on flexural perfor-
mance of the specimens.
6.4. Relative slip at beam end
As a consequence of the shear force transferred by the shear 7.1. Influence of slab thickness
studs, slip between the concrete slab and steel beam was observed
at ends of each specimen. Fig. 13 shows the beam end slip mea- Specimens CB1, CB2 and CB3 all had PPCDs. As listed in Table 1,
sured at different levels of mid-span bending moment. As shown, they had the same amount of reinforcement and same geometries
for a given mid-span bending moment, the slip at beam end varies except that their concrete slab thicknesses were in increasing order
from specimen to specimen. However, no significant differences in (130 mm, 140 mm and 150 mm, respectively). As listed in Table 4,
H. Hou et al. / Engineering Structures 126 (2016) 405416 413
(a) strain profiles across the entire beam section (b) strain profiles across the entire beam section
(at midpoint of CB7) (at midpoint of CB8)
(c) strain profiles across the concrete slab (d) strain profiles across the concrete slab
(at one loading point of CB7) (at one loading point of CB8)
Table 6
Strain data at the pure-bending portion of the specimen under critical bending
moments (unit: 103).
Fig. 14. Moment deflection curves of specimens CB1, CB2 and CB3.
250
Mid-span bending moment (kN.m)
200
150
100
Fig. 15. Moment deflection curves of Specimens CB1, CB4, CB5 and CB6.
7.2. Influence of overlap width
Fig. 16. Moment deflection curves of Specimens CB1, CB9 and CB10. Fig. 18. Moment deflection curves of Specimens CB1 and CB12.
Specimens CB1 and CB11 are identical except that their PPCD
ribs were oriented along two different orthogonal directions.
Fig. 17 shows the mid-span bending moment vs. mid-span deflec-
tion curves of these two specimens. As shown, although these two
specimens eventually achieved similar ultimate flexural resis-
tances, the flexural rigidity of Specimen CB11 is lower than that
of Specimen CB1. This is primarily due to the fact that the ribs
when oriented along the beam longitudinal direction do not pro-
vide sufficient doweling action for the cast-in-place concrete slab,
which could lead to sliding deformation of the cast-in-place con-
crete slab relative to the underneath PPCDs.
8. Conclusions
7.4. Influence of longitudinal reinforcement ratio
This research team conducted an experimental investigation on
Specimens CB1, CB9 and CB10 are only different in that their twelve steel-concrete composite beams. The tested specimens
longitudinal reinforcement ratios are in increasing order (0.29%, included eleven composite beams with cast-in-place concrete slabs
0.46% and 0.65%, respectively). Fig. 16 compares the mid-span on PPCDs and one with a full-depth cast-in-place concrete slab.
bending moment and mid-span deflection curves of these speci- Based upon the test results obtained, the following significant con-
mens. As shown, a specimen with a larger longitudinal reinforce- clusions were drawn:
ment ratio tends to be stiffer even after it is loaded beyond the
limit associated with yielding in the steel beam. However, it is The composite beams consisting of cast-in-place concrete slabs
found that the ultimate flexural resistance does not differ signifi- on PPCDs overall exhibited desirable and stable flexural
cantly among these specimens. performance. At the ultimate state, failure mode of the beams
416 H. Hou et al. / Engineering Structures 126 (2016) 405416
is characterized by the crushing of concrete slab and yielding of However, any opinions, findings, conclusions and recommenda-
steel beam. The beam mid-span bending moment vs. deflection tions presented in this paper are those of the authors and do not
curves exhibit the typical bilinear flexure-dominated trend. Test necessarily reflect the views of the sponsors. Finally yet impor-
results confirm that a composite beam with cast-in-place con- tantly, the authors wish to thank three anonymous reviewers for
crete slab on PPCDs, if designed properly, can have the same ini- their careful evaluations and insightful comments that helped
tial flexural stiffness and ultimate flexural resistance as the one improve the paper.
having the same design parameters but a full-depth cast-in-
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