Flush End Research Articles

Experimental and Numerical Investigations of the Behavior of Flush End Plate Connections at Elevated Temperatures

This paper reports on a set of test results on flush end plate connections at ambient and elevated temperatures. The experiments aimed to investigate the behavior of connections at the ends of unprotected beams in fire situations, when they may be subjected to significant tying forces and large rotations at elevated temperatures, as a consequence of high beam deflection. A change in first fracture mode was observed with increasing temperature as the failing component became the bolts rather than the end plate as the strength of bolts reduces faster than that of steel in fire. At elevated temperatures, the use of thicker end plates can enhance the peak resistance, but reduces the rotational capacity of the connection. Finite-element analyses were performed to simulate the tested connections, and gave predictions very close to the observed behavior of the connections in both the loading and the postpeak resistance phases for all the tests at high temperatures. Via these simulations, minor cracks in the end ...

Hysteretic behaviour of flush end plate joints to concrete-filled steel tubular columns

The results of an experimental research study involving the testing of four bolted moment-resisting connections under simulated seismic loading conditions are presented. Each test specimen modeled the interior joint of a moment-resisting frame consisting of H-shaped steel beams and circular or square concrete-filled steel tube (CFST) columns using high-strength blind bolts. In order to investigate the seismic behaviour of the blind bolted flush end plate joints to CFST columns, the hysteretic performance, failure modes, stiffness degradation and energy dissipation of the connection type are evaluated in detail. The test parameters varied included the column section type and the thickness of the end plate. The experimental results indicate that both the blind bolted connections with circular and square sections exhibited excellent hysteretic behaviour in terms of their moment–rotation response, strain distributions and energy dissipation. Under cyclic loading, all tested specimens displayed large rotation ductility capacities, and the failure modes were similar to those under monotonic loads. The effects of cyclic loading on the behaviour of the composite joint were obvious, especially on load bearing and stiffness of the connections. The joint type exhibited excellent seismic performance, so that it can be effectively utilized in moment-resisting composite frame structures.

Behaviour of flush end plate joints to concrete-filled steel tubular columns

This paper presents the results of an experimental program for bolted moment connection joints of circular or square concrete filled steel tubular (CFST) columns, and H-shaped steel beams using high-strength blind bolts. In order to investigate the static performance and failure modes of the blind bolted connection, an experimental program was conducted involving four sub-assemblages of cruciform beam-to-column joints subjected to monotonic loading. Moment–rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. The test parameters varied were the column section type and the thickness of the end plate. The results showed that the proposed blind bolted connection, which behaves in a semi-rigid and partial strength manner according to the EC3 specification, displays reasonable strength and stiffness. The rotation capacity of this type of connection to square or circular CFST columns exceeds 70 mrad and this satisfies the ductility requirements for earthquake-resistance in most aseismic regions. The blind bolted connection is shown to be a reliable and effective solution for moment-resisting composite frame structures.

An alternative design for internal and external semi-rigid composite joints. Part I: Experimental research

An experimental program has been carried out to test and characterize an innovative design for internal and external semi-rigid composite joints. Three tests are performed on semi-rigid composite joints with flush end plates. One of the tests deals with an internal joint with asymmetric loads, and the other two with external joints. When compared with the usual configuration of this type of joint, the proposed alternative design introduces an innovation which consists in inserting the central reinforcement bars through the column flanges in order to achieve an improved behaviour. In addition, in the case of external joints, the cantilever normally needed to ensure sufficient anchorage length for the reinforcement can be dispensed with. The experimental results are used to calibrate the finite element models. These are used to conduct a parametric study and to propose some modifications to the Eurocode 4 component method, as can be seen in the companion paper.

Testing of semi-rigid steel–concrete composite frames subjected to vertical loads

A pair of tests carried out on full-scale semi-rigid composite frames with two stories and two bays are reported. The composite frames undergoing tests are composed of steel columns and steel–concrete composite beams. The beam-to-column connection consists of a flush end plate welded to the beam end and bolted to the column flange. To investigate the influences of semi-rigid connections and composite action of the slab on the performance of the steel frames, the overall response of the frame specimen, the connection behavior, and the beam’s behavior when subjected to vertical loads have been measured and analyzed. The nonsymmetrical loading effect is also considered. It is found that the composite endplate connection, which is semi-rigid and of partial strength, has reasonable strength and stiffness, and its rotation capacity satisfies the ductility requirement of no less than 30 mrad for earthquake-resistance. The effects of the flexibility of the connections and the composite action of the slab on the strength, stiffness, and ductility of steel frames must be properly considered in the design.

The effects of partial shear connection in composite flush end plate joints Part I — experimental study

The experimental results of partial shear connection composite beams subjected to hogging bending have been previously reported. An extension to this work which considers the presence of a semi-rigid, partial strength connection is described herein. Five sub-assemblages of cruciform composite joints that simulate the internal region of a semi-continuous frame were tested. The joints were constructed using a novel approach of blind bolting a flush end plate to concrete-filled square hollow columns. Apart from the level of shear connection, the other parameter varied was the reinforcement area. In addition, a bare steel joint was also tested to act as comparison specimen. Based on the experimental results, the intrinsic behaviour of the joints in terms of strength, stiffness and ductility was assessed. It was further affirmed that by lowering the levels of shear connection, the rotation capacity of the composite joints was enhanced with only a slight compromise if the stiffness and moment resistance. A notable effect on the connection behaviour was also observed by varying the reinforcement levels. The outcomes clearly affirmed the benefits of partial shear connection in contributing the additional flexibility to increase the joint ductility, which is extremely advantageous for plastic design purposes. In view of this, the current restriction of providing full shear connection design within hogging moment regions of continuous and semi-continuous structures could be relaxed.

The effects of partial shear connection in composite flush end plate joints Part II—Analytical study and design appraisal

The behaviour of composite beams under hogging bending has been successfully simulated using an analytical model derived previously. This paper describes the extension of the work to study the behaviour of composite joints incorporating semi-rigid flush end plate connections. With proper inclusion of the joint characteristics, the model was found to be equally capable of modelling the structural behaviour including the effects of partial shear connection. Experimental results of a novel series of composite joint tests detailed in the accompanying companion paper were compared, in addition to those published in the literature. The analysis results provided close agreement with the various test behaviour. Using the model that has been properly calibrated against experimental results, a systematic parametric study was also undertaken. The outcomes are described herein. In addition, existing design models to predict the strength, stiffness, and ductility of composite joints were also reviewed and compared against the test results. The results emanating from this paper contribute as a total package apart from experimental undertakings to further understand the complex behaviour of the composite joints. This is very beneficial in a design perspective.

Testing of steel–concrete composite connections and appraisal of results

This paper presents results obtained from tests carried on six full-scale composite beam-to-column joints. The steelwork connection consists of a flush end plate welded to the beam end and bolted to the column flange. The steel beam section and concrete slab remained identical for all six specimens. Three types of column are used: bare steel, partially encased and fully encased columns. Other variables include the area of reinforcement in the slab and the presence of stiffeners in the column web. Moment–rotation curves obtained from the tests are compared with those predicted by an analytical model. Plastic analysis of cross section is used to develop the analytical model for the prediction of moment capacity. A simple spring model for the slab combined with that of the steel joint model, as proposed in Revised Annex J of EC3, is used to assess the stiffness of the composite joints. Generally, the proposed model can predict the moment capacity of composite joints with good accuracy. However, the model tends to over predict the rotational stiffness.

Performance of composite connections: Major axis end plate joints

Abstract The results of a series of five tests on composite beam-to-column connections are reported. The steelwork part of the connection used an end plate, welded to the beam and bolted to the column flange. For comparison, a sixth test was on a bare steel connection of the same type. Increasing the amount of reinforcement caused a rise not only in moment resistance but also in the rotation capacity of the composite connection. A similar result was obtained by replacing a flush end plate by an extended one. Increase in the depth of the steel section decreased rotation capacity. Plastic analysis of the composite connections, with forces in tension bolts predicted by Annex J of Eurocode 3, provides satisfactory prediction of moment resistance. Good rotation capacity in hogging bending is associated with a plastic neutral axis for the composite beam being in the top flange of the steel section. Large deformation of the lower part of this section by local buckling is the preferable failure mode, because no sudden drop in resistance occurs. A simple spring model can be used to predict satisfactorily a bilinear approximation of the moment-rotation curve, provided account is taken of the deformation of the shear connection.

Studies on restriction endonucleases of acetic acid bacteria and allied organisms. Part. IX. Purification and properties of restriction endonuclease from Deleya marina IAM 14114, a marine bacterium (dmaI).

A restriction endonuclease, designated as DmaI, was purified from cell-free extracts of Deleya marina IAM 14114 by streptomycin treatment, ammonium sulfate fractionation and two steps of chromatographies on heparin-Sepharose CL-6B and Mono Q (HR 5/5, FPLC). The purified enzyme was homogeneous on SDS-polyacrylamide gel disk electrophoresis and a ligation-recutting test. The relative molecular mass measurements of the purified enzyme gave 28,000 daltons by SDS-polyacrylamide gel disk electrophoresis and 56,000 daltons by gel filtration. These data indicated that the purified enzyme (56,000 daltons) has a dimeric structure composed of two 28,000-dalton subunits. The isoelectric point was 5.5. The purified enzyme worked best at 37 degrees C in a reaction mixture (50 microliters) containing 1.0 micrograms lambda DNA, 10 mM Tris-HCl, 7 mM 2-mercaptoethanol, 7 mM MgCl2 and 100 mM NaCl (pH 7.5). The enzyme was stable up to 55 degrees C and between pH 7.0 and 9.0. The purified enzyme recognizes the palindromic hexanucleotide DNA sequence 5'-CAGCTG-3', cuts between G and C and produces a flush end (isoschizomer of PvuII).

Specific binding of transposase to terminal inverted repeats of transposable element Tn3.

Tn3 transposase, which is required for transposition of Tn3, has been purified by a low-ionic-strength-precipitation method. Using a nitrocellulose filter binding assay, we have shown that transposase binds to any restriction fragment. However, binding of the transposase to specific fragments containing the terminal inverted repeat sequences of Tn3 can be demonstrated by treatment of transposase-DNA complexes with heparin, which effectively removes the transposase bound to the other nonspecific fragments at pH 5-6. DNase I "footprinting" analysis showed that the transposase protects an inner 25-base-pair region of the 38-base-pair terminal inverted repeat sequence of Tn3. This protection is not dependent on pH. Interestingly, binding of the transposase to the inverted repeat sequences facilitates DNase I to nick at the end of the Tn3 sequence. It was also observed that the transposase protects the end regions of restriction fragments with a cohesive sequence at their 5' end or with a flush end from DNase I cleavage. The specific and nonspecific binding of transposase to DNA is ATP-independent.

The effects of partially filled polyethylene tube intraosseous implants in rats

Polyethylene tubes obturated flush at one end and 1 mm. short at the opposite end with gutta percha and Grossman's cement as the cementing media were implanted in rat tibias. The gutta-percha, the set Grossman's cement, and the polyethylene implant were well tolerated by the rat intraosseous tissues. There was no significant inflammatory response at either the flush end or the short end of the polyethylene implant.

Construction of plasmids carrying the cI gene of bacteriophage lambda.

By techniques of recombination in vitro, we have constructed a plasmid bearing the repressor gene (cI) of bacteriophage lambda fused to the promoter of the lac operon. Strains carrying this plasmid overproduce lambda repressor. This functional cI gene was reconstituted by joining DNA fragments bearing different parts of that gene. Flush end fusion techniques, involving no sequence overlap, were necessary for the construction; in certain cases, the abutting of the DNA molecules bearing ends generated by different restriction endonucleases creates a sequence at the junction which is recognized by one of the restriction endonucleases.

Durability of Prestressed Concrete Beams

The durability of pretensioned and posttensioned concrete beams is being studied using laboratory-prepared beam specimens. A group of beams containing pretensioned strands, some made with airentrained concrete and others with non-air-entrained concrete, was exposed to natural weathering. Sixteen beams were subjected to freezing in air and thawing in seawater at Treat Island, Maine, and three beams were exposed to sulfate attack in warm seawater on the Florida coast. In Maine the nonair-entrained concrete beams failed during the first winter; the air-entrained beams remain in good condition after five winters. No significant results have been observed at the Florida exposure. A group of posttensioned beams, all made with air-entrained concrete, was also exposed in Maine. Four posttensioning systems with either external or flush end anchorages, and 12 types of end-anchorage protection were used. The auxiliary steel reinforcement had a nominal 3/a in. concrete cover. After two winters of exposure, two of 40 end-anchorage protections have become detached, two have become loose, and several have developed a narrow crack at the bond with the beam. In all of the beams that show evidence of failure, portland cement concrete was used to enclose external anchorages. It is concluded that (1) Concrete for prestressed structural elements that are to be exposed to freezing and thawing in a moist condition should contain entrained air. (2) The concrete cover over reinforcing should be greater than '3/a in. when exposure to seawater is involved. (3) Epoxy concrete is superior to portland cement concrete for end protection. Flush anchorages appear to be more effectively protected than external anchorages.