Polyethylene terephthalate (PET) is one of the most prevalent transparent thermoplastics. It is commonly utilized due to its low cost and high durability. With the massive accumulation of waste PET, ...however, serious environmental pollution has become a global problem. Compared to traditional chemical degradation, biodegradation of PET catalyzed by PET hydrolase (PETase) is more environmentally friendly and energy-efficient. BbPETasesup.CD from the Burkholderiales bacterium is a PETase that shows favorable properties for application in the biodegradation of PET. To enhance the enzymatic performance of this enzyme, this work focuses on the rational design of disulfide bridges in BbPETasesup.CD. We utilized two computational algorithms to predict the probable disulfide-bridge mutations in BbPETasesup.CD, and five variants were acquired from the computations. Among these, the N364C/D418C variant with one additional disulfide bond showed higher expression than the wild-type enzyme (WT) and the best enzymatic performance. The melting temperature (Tm) of the N364C/D418C variant presented an increase of 14.8 °C over that of WT (56.5 °C), indicating that the additional disulfide bond significantly raised the thermodynamic stability of the enzyme. Kinetic experiments at different temperatures also demonstrated the thermal stability increase of the variant. The variant also showed significantly increased activity over WT when using bis(hydroxyethyl) terephthalate (BHET) as the substrate. More remarkably, the N364C/D418C variant exhibited approximately an 11-fold increase over the WT enzyme in the long-term (14 days) degradation of PET films. The results prove that the rationally designed disulfide bond significantly improved the enzymatic performance of the enzyme for PET degradation.
AbstractPrefabricated reinforced concrete column connections employing grouted sleeve (GS) splices enable rapid construction, are familiar to contractors, and their detailing resembles cast-in-place ...(CIP) construction. Previous studies showed disrupted plastic hinge formation in the stiff sleeve region. The proposed design method shifts the plastic hinge location above the sleeve region, which effectively increases the plastic rotation capacity and ductility. Plastic hinge shifting was realized by using transition splicing and high-strength steel reinforcement in the connecting element (footing). The proposed method was investigated experimentally using two 0.42-scale column tests under slow cyclic loading and a series of uniaxial tensile tests. Results indicate that good ductility can be achieved compared with conventional CIP construction and previously tested GS connections details. Experimental and analytical moment-curvature results were used to support discussion of design considerations and of an approximate method for calculating the displacement ductility of precast columns with GS connections and shifted plastic hinging.
AbstractReinforcing bar couplers are used in prefabricated bridge elements and bridge systems for accelerated bridge construction. Grouted splice sleeve connectors are used in bridge substructures ...because of the enhanced construction tolerances they offer. This paper presents a simplified modeling strategy for seismic assessment of precast bridge columns connected to precast footings using grouted splice sleeve connectors. A computational model was developed and validated using three half-scale bridge subassemblies tested to failure. Cyclic quasi-static loading was applied to two precast subassemblies and one cast-in-place specimen. The connectors were located in the footing, for the first precast alternative, and in the column end for the second precast alternative along with debonding of reinforcing bars in the footing. Force-based beam-column elements with fiber sections were used to construct the computational model based on plastic hinge weighted integration; the model included low-cycle fatigue and bond-slip. The proposed model was validated with the experiments through both local and global response comparisons. The results from the proposed computational model were found to be in good agreement with the experiments.
Abstract
Ultrahigh-performance concrete (UHPC) offers significant potential to address a variety of needs in bridge design, construction, and performance enhancement. Bridge owners have shown ...willingness to embrace novel solutions that could address specific challenges related to the cost, speed of construction, durability, and service life of their projects. There are hundreds of bridges worldwide that, largely in the past decade, have utilized UHPC. These applications range from minor field-cast closures to precast segments for long-span bridges to kilometer-long bridge deck overlays on a signature structure. The objective of this paper is to promote the application of this class of cementitious material in bridge engineering by presenting the progress that has been made in different regions of the world in the past two decades. Today, UHPC is being widely used in Malaysia to design and construct many bridges of different types and spans as they build out their roadway network. In South Korea, the unique characteristics of UHPC are being utilized to advance the state-of-the-art in long-span bridges. The French were early adopters and pioneers in building a strong foundation for using UHPC in a variety of bridge applications. In Switzerland, UHPC is employed to address major bridge rehabilitation needs. The United States bridge sector has embraced UHPC for a variety of field-cast connections. Current research and development efforts are promoting the use of UHPC in major rehabilitation projects and construction of primary bridge components. The adoption of UHPC solutions into the bridge sector is progressing rapidly because of the unique opportunities provided by the strength and durability of the material. It is expected that additional innovations and refinements of solutions will occur as knowledge of the material proliferates.
For photovoltaic polymers with a D-π-A backbone, there are a great deal of D and A units, but the choice of π bridge is relatively limited and thiophene (T) is still the most effective one. Here, we ...utilize two D-π-A polymers,
J52-FS
with thiophene as the π bridge and
PE2
with thieno3,2-
b
thiophene (TT) as the π bridge, to combine with a low band-gap non-fullenere
Y6
, respectively. The photovoltaic cells based on
PE2
:
Y6
can realize a PCE of 13.50%, which is obviously higher than the 10.58% PCE of the
J52-FS
:
Y6
analogue. Our work demonstrates that using TT as the π-bridge is a simple and promising approach to construct efficient photovoltaic polymers.
The photovoltaic cells of
PE2
with a thieno3,2-
b
thiophene (TT) π bridge realized a PCE of 13.50%, obviously higher than the 10.58% PCE of
J52-FS
with a thiophene π bridge.
•Seismic behavior of 1:3-scale UHPC-filled column-to-footing socket connection.•The difference of the cyclic response between the precast column and CIP column.•A FEM to consider the rotation effect ...of the column embedded in the footing.
Accelerated bridge construction (ABC) has been paid great attention in China for the significant advantages compared with cast-in-place (CIP), such as higher construction speed, less environmental impact and structural members of higher quality. However, the reliability, durability and seismic behavior of the connection between prefabricated bridge column and the rest of the structure are primary factors that limit the application of the ABC in the moderate and high seismic zones. In this study, quasi-static experimental investigation of seismic performance of three 1:3-scale ultra-high performance concrete (UHPC)-filled socket reinforced concrete (RC) column-foundation connection specimens were conducted. A fiber-based finite element model is developed considering the rotation effect of the column embedded in the footing. The seismic behavior of the precast column specimens with UHPC-filled socket connection type was compared with that of CIP specimen. The experimental and numerical results show that the damage evolution, failure modes and hysteretic responses of the precast bridge column are equivalent with those of the CIP bridge column. Numerical analysis also validated that the finite element model(FEM) in this paper is adequate to predict seismic response of the precast column with UHPC-filled socket connection. The UHPC-filled socket connection is a reliable connection type in prefabricated column-foundation connection joint which is suitable for moderate and high seismic regions.
Ultra-high-performance concrete (UHPC) is attracting increasing interests worldwide due to its superior mechanical properties and durability. Securing proper rheological properties can affect fiber ...dispersion and alignment with marked effect on UHPC performance. Tailoring the rheological properties of UHPC to secure enhanced performance is not widely considered in the mixture design stage. In this paper, an overview of the rheological properties of UHPC, applicable flow models, measurement techniques and errors associated with the interpretation of rheological measurements are discussed. The effect of various constituent materials on rheological properties of UHPC is presented. This includes the cementitious materials, sand, chemical admixtures, fibers, nanomaterials, and internal curing agents. Most importantly, the paper discusses the rheological properties requirements of UHPC and strategies to control rheology of UHPC targeted for different applications, such as repair and rehabilitation, bridge deck panel connections, construction of structural and architectural elements, and digital fabrication.
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