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Concrete creep and shrinkage at cold temperatures are less significant than those at room temperature. For the structures exposed to subarctic weather, in situ creep and shrinkage strains are important factors in design process, such as estimating pre-stress losses, since ambient temperature and relative humidity change in a wide range. In the present study, the in situ creep and shrinkage strains were measured from high strength concrete specimens loaded in a concrete creep frame exposed to subarctic weather for 332 days. The measured creep strain was 23–30% of creep strain from specimens at room temperature. Also, the shrinkage strain was 67% of the shrinkage strain measured at room temperature. The comparison showed that the creep and shrinkage strains in real subarctic weather were larger than strains at a sustained cold temperature, but they were substantially smaller than strains at room temperature. The measured strains were compared with predicted values from widely used creep and shrinkage models. The AASHTO-LRFD model and the CEB MC90-99 model matched well with test results.

This study was to investigate the concrete creep and shrinkage of early-age concrete at cold temperatures and to analyze their characteristics compared with the creep and shrinkage measured at room temperature. Concrete creep frames were used to apply a sustained force to specimens. One frame was located in a laboratory at room temperature, and the other was in a cold room. An MTS test machine with an environmental chamber was used to test other specimens at the same time with an improved accuracy in force and temperature control. Test results showed that the concrete creep and shrinkage stayed dormant at the cold temperature (−40°C and −55°C). But the creep and shrinkage resumed once the temperature increased from the cold to room temperature. The concrete creep and shrinkage strain change pattern was similar to the one measured from specimens at room temperature. When concrete was loaded at the cold temperature and the temperature changed from the cold to room temperature, there was a substantial increase in strain as the temperature changed. The accumulated creep and shrinkage were greater than the ones measured from the specimen placed in room temperature.

The seismic behavior of Tire Derived Aggregate (TDA) used as backfill material of 6.10 m high retaining walls was investigated based on nonlinear time-history Finite Element Analysis (FEA). The retaining walls were semi-gravity reinforced concrete cantilever type. In the backfill, a 2.74 m thick conventional soil layer was placed over a 3.06 m thick TDA layer. For comparison purpose, a conventional all soil-backfill model was also developed, and the analysis results from the two models under the Northridge and Takatori earthquakes were compared. The FEA results showed that both models did not experience major damage in the backfill under the Northridge earthquake. However, under the Takatori earthquake, the TDA-backfill model developed substantially large displacement in the retaining walls and in the backfill compared with the soil-backfill model. Regions of large plastic strain were mainly formed in the TDA layer, and the soil over the TDA layer did not experience such large plastic strain, suggesting less damage than the soil-backfill model. In addition, the acceleration on the backfill surface of the TDA-backfill model decreased substantially compared with the soil-backfill model. If an acceleration sensitive structure is placed on the surface of the backfill, the TDA backfill may induce less damage to it.

The quality of grout becomes more important as many projects utilize precast concrete elements and systems to accelerate the delivery of a project. Also, the use of high-strength grout materials increases to properly connect high-strength concrete members. In the present study, two high-strength, cementitious grout materials were tested for their compressive strength to estimate a coefficient of variation (cv), to investigate effects due to curing condition and initial curing time, and to evaluate the strength ratio between cube and cylinder specimens. The 28-day strength of tested grouts reached more than 62.1 MPa (9,000 psi). The estimated cv was 2.3 %, which was slightly higher than the value of 2.1 % used in ASTM C109, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50 mm] Cube Specimens). Based on the estimated cv, the variability limits of compressive strength in ASTM C109 can be 9.5 % (from 8.7 %) for three cubes and 8.4 % (from 7.6 %) for two cubes. There was not a substantial difference in compressive strength between water-cured and moist-cured cubes. Also, the difference of compressive strength is minimal between cubes initially cured for 24 hours and 48 hours before demolding. The compressive strength ratio of ϕ100 mm × 200 mm cylinder specimens to 50 mm cube specimens was between 0.78 and 0.90 for different test ages. The mean ratio was 0.83. These observations can help engineers and practitioners to use ASTM C109 and ASTM C1107, Standard Specification for Packaged Dry, Hydraulic-Cement Grout (Nonshrink), with more confidence when they test high-strength, cementitious grout materials.

Dynamic Ratcheting (DR) is a phenomenon in which plastic deformation in a hysteretic damping system increases asymmetrically in successive cycles. In the present paper, DR in single degree-of-freedom (SDOF) systems under earthquake excitation is investigated based on strong motion data collected in California between 2002 and 2012. The characteristics of earthquakes in the time–frequency domain are studied on spectrograms; furthermore, linkages between the spectrogram, displacement time history, and the Fourier Transform are identified to locate intervals during which DR is expected to occur. It is observed that DR occurs for 10 out of 160 studied earthquakes according to the proposed DR investigation procedure. The likelihood of DR seems to mainly depend on local site conditions; however, the likelihood significantly increases as the magnitude of earthquakes increases.

Tire Derived Aggregate (TDA) is a recycled lightweight construction material produced by cutting waste tires. The present research aims at evaluating the dynamic performance of TDA backfill under simulated earthquakes based on a full-scale shake table test. Main test results such as accelerations, wall displacements, and dynamic pressures are presented and discussed in this paper. A comparison with a similar shake table test of a wall with conventional soil backfill shows that the amount of wall sliding increased but the dynamic pressure on the wall exerted by the TDA backfill substantially decreased.

Transverse live load distribution in a concrete–fiber-reinforced polymer (FRP) composite hybrid bridge was investigated both experimentally and analytically. The subject bridge was a concrete–FRP composite hybrid bridge, constructed with four 31-ft (9.4-m) long, prefabricated superstructure panels, which were joined along longitudinal field joints made of steel-reinforced grout. The live load distribution factors (DFs) of this bridge were evaluated with strain values measured in field tests and produced from finite element analysis. Design documents and load rating reports showed that a simplified method on the basis of beam-bending could be used in the design process, which required live load DFs. From strain values measured during load tests, the DFs were inferred to be 0.35 and 0.49 for interior and exterior panels, respectively. The comparison of load tests done 6 years apart indicated no significant change in the structural performance of the bridge. Although the design of this structure was unique, the evaluation showed that other hybrid structural members also could achieve good load distribution. The investigation indicated that composite structures could be durable with little maintenance required.

Tire derived aggregate (TDA) is a recycled fill material produced by cutting scrap tires into pieces ranging in size from 12 to 305 mm. For the last two decades, TDA has been successfully used in various projects such as embankments, bridge abutments, subgrade insulation for roads, vibration mitigation for rail lines, and landfill daily cover. The material properties of TDA are necessary for the planning and design of such projects; however, there is limited information available, especially for large-size TDA (maximum particle size ≥75 mm). Large-size TDA is typically used as lightweight fill material for embankments, foundations, and retaining walls. In this paper, the material properties of large-size TDA, as collected from published sources and recently completed material tests, are presented and discussed. These properties include unit weight, shear strength, compressibility, and lateral earth pressure coefficient. In addition, several civil engineering projects are discussed and compared to...

A nonlinear model-based system identification method is proposed, formulated, implemented, and applied to a three-span continuous base-isolated bridge. Transverse and rotational rigid-body motions of the bridge superstructure are formulated into two degrees-of-freedom dynamic governing equations. To model hysteretic behavior of lead–rubber bearings, the Menegotto–Pinto model is used. The proposed system identification procedures consist of two phases to address ill-conditioning issues. The uncertainty of parameters is considered, which results in probability distributions instead of single values for identified parameters. The proposed system identification is adopted in the comparison of experimental data sets. Hypothesis testing is used to determine the closeness of identification results. The proposed method is applied to quick-release field experiments on the bridge to investigate aging and temperature dependent effects in lead–rubber bearings.

Currently, the AASHTO-LRFD design code specifies the same effective slab width design criteria for both positive moment sections and negative moment sections. The only difference in computing effective slab width between the positive and negative moment regions is the value of effective span length ( Le ) , the definition of which is problematic. The effective slab width concept for the positive moment regions has been investigated by many researchers. However, the classical effective slab width definition does not take into account both the strain variation through the slab thickness and the mechanism that redistributes load from concrete to steel reinforcement after cracking. In this paper, a more robust effective slab width definition for the negative moment section is introduced to account for these factors. The proposed definition is developed for negative moment regions and explored by using the finite-element method (FEM). The finite-element modeling scheme is briefly discussed, and the model is su...

In a composite section, in-plane shear strain in the slab acting as a flange in the composite girder under the applied bending causes the longitudinal displacements in the parts of the slab remote from the webs to lag behind those near the webs. This phenomenon, termed shear-lag, can result in an incorrect calculation of the displacement and extreme fiber stresses when using only the elementary theory of beam bending. The effective width concept has been introduced, widely recognized, and implemented into different codes of practice around the world as a simplified practical method for design and evaluation of structural strength and stiffness while accounting for shear-lag effects indirectly. Each code implements different ideas and approaches for specifying effective width. This paper proposes simpler and more versatile design criteria for computing the effective width beff in steel-concrete composite bridges. A parametric study was conducted based on finite-element analysis of bridges selected by a statistical method—namely, design of experiment concepts. Both simple-span and multiple-span continuous bridges were considered in the parametric study. The finite-element methodology was validated with companion experiments on 1/4- and 1/2-scale specimens. Effective width values at the critical sections were computed from stresses extracted from FEM models and used in developing candidate design equations. The final design criteria were selected based on assessment of impact of candidate equations. Use of full width—the most versatile, simplest, and sufficiently accurate effective width design criteria, is proposed for both positive and negative moment regions.

In dynamic analysis, hysteretic damping often provides a reasonable model of the inelastic behavior of a structure. Nonlinearity presented by hysteretic damping, however, introduces the possibility of developing complicated motions not expected in linear dynamics. In this study, motions of a single-degree-of-freedom system with hysteretic damping under dual-frequency sinusoidal excitations are investigated through numerical simulation. Hysteretic damping behavior is represented by three different plasticity models: the elasto-perfectly-plastic model; the linear kinematic hardening model; and the two-surface model. Under certain conditions, the resultant motions from the elasto-perfectly-plastic model and the two-surface model exhibit a continual increment of plastic deformation in successive cycles. Parametric study shows that this dynamic ratcheting develops when applied frequencies are commensurable (i.e., related to each other with integer ratio), and the product of terms comprising the ratio is an eve...

The cyclic performance of an unbonded precast concrete segmental bridge column system is examined in this paper. This system uses unbonded posttensioning to enhance the self-centering capability and mild steel reinforcement extended across the segment joints to enhance the energy dissipation capability. A simplified analytical method for the system under lateral load is established, and the simplified analytical results are compared with those obtained from the three-dimensional (3-D) finite element method (FEM). On the basis of the simplified analytical method, suggestions are made about both the height of the column to which the mild steel should be continued from the foundation and the limitation of the steel ratio to minimize residual displacement. With the steel ratio varied, the correlation between the energy dissipation capability and the self-centering capability of this system is investigated by means of the 3-D FEM. From simulation results, it was found that both the energy dissipation and the residual displacement increase as the steel ratio increases. It was also found that the system with a steel ratio suggested by the proposed equation resulted in a significant increase in energy dissipation compared with the one without mild steel across the joints, while the recommended system maintained a small residual displacement after loading reversals.

This paper presents experimental results of the ultimate behavior of the negative moment region of a quarter-scale full model and a half-scale subassemblage model of a two-span continuous composite bridge of concrete deck slab on steel girder. The two specimens are based on a prototype bridge that has a large girder spacing [3,800 mm (13 ft)]. At the ultimate state, it is shown that a larger portion of the deck is activated to resist tensile stress compared with the effective width specified in the AASHTO load and resistance factor design bridge specifications. Also, a plastic hinge that forms at the internal support has enough rotational capacity (ductility) to enable development of a second plastic hinge within the span. Experimental results show a reasonably good match with accompanying finite element method analyses.

A composite section is made up of a steel girder and concrete slab connected by shear connectors. The shear lag phenomenon usually takes place in such a section and results in underestimation of stresses and strains at the web-to-flange intersections of the girder. With the introduction of the concept of effective slab width, the actual width can be replaced by an appropriate reduced slab width. The classical effective slab width definition does not take into account the strain variation through the slab thickness. More sophisticated definitions are introduced and used with finite element analyses. The method of finite element modeling is discussed, and the model is successfully verified with experimental results. Parametric study is conducted to investigate the effective slab width for both positive and negative moment sections. The effective slab width is computed and compared with the current AASHTO load and resistance factor design (LRFD) specifications. The results demonstrate that full width can be used as the effective slab width in the design and analysis in most cases for the design and analysis of both positive and negative moment sections. The current AASHTO LRFD specifications are found to be conservative for configurations with widely spaced girders, especially in negative moment sections.

This paper presents experimental results of the ultimate behavior of the negative moment region of a quarter-scale full model and a half-scale subassemblage model of a two-span continuous composite bridge of concrete deck slab on steel girder. The two specimens are based on a prototype bridge that has a large girder spacing [3,800 mm (13 ft)]. At the ultimate state, it is shown that a larger portion of the deck is activated to resist tensile stress compared with the effective width specified in the AASHTO load and resistance factor design bridge specifications. Also, a plastic hinge that forms at the internal support has enough rotational capacity (ductility) to enable development of a second plastic hinge within the span. Experimental results show a reasonably good match with accompanying finite element method analyses.

A composite section is made up of a concrete slab attached to a steel girder by means of shear connectors. Under positive bending moment, part of the slab will act as the flange of the girder resis...

In the analysis and design of steel–concrete composite girders of a bridge, deflections, stresses, and strengths are typically obtained from elementary beam bending theory by utilizing the effective flange width concept. Shear lag effects are accounted for indirectly, by replacing the actual slab width by an appropriate reduced “effective” width. Besides the exact numerical values that can be given by numerical analysis of a bridge, it is necessary that code provisions should provide simplified practical method of evaluation of effective flange width without significant loss of accuracy. So each code implements different ideas and approaches for specifying effective flange width. Comparing them highlights distinct philosophies underlying the various effective width code formulations, which is the main objective of this paper. In this paper, the effective flange width provisions in the US, Britain, Canada, Japan, and European Committee are presented and compared. Characteristics of each provision are briefly described and summarized. Numerical comparisons for simply-supported spans and negative moment regions of continuous spans follow. The paper concludes with a summary outlining the commonalities and main differences among all these provisions.

This closure article was written in response to a commentary on recent research (Chiewanichakorn et al, 2004) that investigated composite sections (made up of a concrete slab attached to a steel girder by means of shear connectors). The commentary author maintained that formulas like the one proposed by the researchers tend to produce increasing effective widths with decreasing interaction between beam and slab. The discusser also pointed out that the researchers' comparison of interior and exterior beam specimens can be slightly misleading, since all beams were T-shaped. The discusser concludes that the foremost reason for maintaining the present limitations on effective width is that concrete cracks. Composite beams have become notorious for developing longitudinal cracks in the concrete slabs over their steel beam sections. In their response, the original researchers contend that the discusser's argument is not valid and they stand strongly behind their findings. The researchers point out several major problems with using the girder deflection approach, versus using compressive bending stress. They conclude that the consequence of imposing the discusser's suggested limitations on effective flange width would be underestimation of the section resistance, especially after concrete cracking.

In several successful accelerated bridge construction projects in Florida and Texas, prefabricated bridge pier components have been utilized, which result in significant reduction of the construction schedule. This paper summarizes major accelerated bridge construction projects through adopting pre-fabricated bridge pier components, which shows its popularity in recent years. In particular, details in geometry, reinforcement, and connections from several projects are compared, focusing on their applicability in seismic regions. Systems in seismic regions investigated recently by several research groups are also summarized and compared. As concluding remarks, issues and recommendations regarding connections and reinforcement detailing are summarized.