Experimental monitoring of the strengthening construction of a segmental box girder bridge and field testing of external prestressing tendons anchorage

Prestressed concrete segmental box girder bridges are composed of short concrete segments that are either precast or cast in situ and then joined together by longitudinally post-tensioning internal,external,or mixed tendons.The objectives of this study are to monitor the construction process of the external prestressing tendons to strengthen the bridge structure and perform a field load test to measure the strain and the deflection of the anchorage devices of the external prestressing tendons to determine the state of these devices after tension forces are applied.The monitoring process of the external prestressing tendons construction includes inspecting the cracks in the diaphragm anchorage and the deviation block devices before the tension forces are applied to the external tendons;measuring the deformation of the steel deviation cross beam during the tension process;measuring the deformation of the box girder after different levels of tension forces are applied;measuring the elongation of the external tendons in each level of the tension;and measuring the natural frequency of the external tendons after the tension process is complete.The results of the monitoring process show that the measured values of the deformation,the elongation,and the natural frequency meet the requirements.Therefore,there is no damage during the construction and the tensioning of the external prestressing tendons.A field load test is performed to the anchorage beam,the steel deviation block devices,and the steel deviation cross beam.The field load test results of the anchorage devices show that the values of the strains,the stresses,and the deflection are less than the respective allowable limit values in the requirements.Therefore,the anchorage devices have sufficient strength,and the working state is good after the tension forces are applied to the external prestressing tendons.

Effects of N-Linked Glycan on Lassa Virus Envelope Glycoprotein Cleavage,Infectivity,and Immune Response

Lassa virus(LASV)belongs to the Mammarenavirus genus(family Arenaviridae)and causes severe hemorrhagic fever in humans.The glycoprotein complex(GPC)contains eleven N-linked glycans that play essential roles in GPC functionalities such as cleavage,transport,receptor recognition,epitope shielding,and immune response.We used three mutagenesis strategies(asparagine to glutamine,asparagine to alanine,and serine/tyrosine to alanine mutants)to abolish individual glycan chain on GPC and found that all the three strategies led to cleavage inefficiency on the 2nd(N89),5th(N119),or 8th(N365)glycosylation motif.To evaluate N to Q mutagenesis for further research,it was found that deletion of the 2nd(N89Q)or 8th(N365Q)glycan completely inhibited the transduction efficiency of pseudotyped particles.We further investigated the role of individual glycan on GPC-mediated immune response by DNA immunization of mice.Deletion of the individual 1st(N79Q),3rd(N99Q),5th(N119Q),or 6th(N167Q)glycan significantly enhanced the proportion of effector CD4+cells,whereas deletion of the 1st(N79Q),2nd(N89Q),3rd(N99Q),4th(N109Q),5th(N119Q),6th(N167Q),or 9th(N373Q)glycan enhanced the proportion of CD8+effector T cells.Deletion of specific glycan improves the Th1-type immune response,and abolishment of glycan on GPC generally increases the antibody titer to the glycan-deficient GPC.However,the antibodies from either the mutant or WT GPC-immunized mice show little neutralization effect on wild-type LASV.The glycan residues on GPC provide an immune shield for the virus,and thus represent a target for the design and development of a vaccine.

Assembly of long DNA sequences using a new synthetic Escherichia coli-yeast shuttle vector

Synthetic biology is a newly developed field of research focused on designing and rebuilding novel biomolecular components, circuits, and networks. Synthetic biology can also help understand biological principles and engineer complex artificial metabolic systems. DNA manipulation on a large genome-wide scale is an inevitable challenge, but a necessary tool for synthetic biology. To improve the methods used for the synthesis of long DNA fragments, here we constructed a novel shuttle vector named p GF(plasmid Genome Fast) for DNA assembly in vivo. The BAC plasmid p CC1 BAC, which can accommodate large DNA molecules, was chosen as the backbone. The sequence of the yeast artificial chromosome(YAC) regulatory element CEN6-ARS4 was synthesized and inserted into the plasmid to enable it to replicate in yeast. The selection sequence HIS3, obtained by polymerase chain reaction(PCR) from the plasmid p BS313, was inserted for screening. This new synthetic shuttle vector can mediate the transformation-associated recombination(TAR) assembly of large DNA fragments in yeast, and the assembled products can be transformed into Escherichia coli for further amplification. We also conducted in vivo DNA assembly using p GF and yeast homologous recombination and constructed a 31-kb long DNA sequence from the cyanophage PP genome. Our findings show that this novel shuttle vector would be a useful tool for efficient genome-scale DNA reconstruction.

Evaluation of the static and dynamic structural performance of segmental pre-stressed concrete box girder bridge after repairing and strengthening

The objectives of this study are to explain the repairing and strengthening methods which are used to improve the structural performance of the bridge structure,to analyze the static and dynamic responses after strengthening,and to evaluate the performance of the bridge structure after repairing and strengthening.The methods of repairing and strengthening include reconstruction the deck of the bridge by casting 10 cm layer of concrete,strengthening the web and bottom floor of box girders of middle spans and side spans by sticking the steel plates,strengthening the whole bridge structure by using external pre-stressing tendons,and treatment the cracks.The results of theoretical analysis show that the values of tensile stress and vertical deflection are decreased and the compressive stress is increased after strengthening.There are not tensile stresses are appeared in the sections of the bridge structure.The modal analysis results show that the value of natural frequency is equal to 2.09 Hz which is more than the values before strengthening which is equal to 1.64 Hz,indicating that the stiffness of the bridge structure is improved and the strengthening process is effective to improve the cracks resistance and bearing capacity of the bridge structure.