Dowel Connections Research Articles

Behavior of Timber-Steel Composite with Dowel Connection under Fire

Recently, a hybrid structure called Timber-Steel Composite (TSC), which is assembled by a central steel I beam with wooden block covered, is expected to introduce a potential strength for the design of modern wooden structure. However, information on this type of structure under the influence of fire is not yet sufficiently explicit to provide designers with a reliable index. The aim of this research was to study the behavior of TSC with dowel connection under fire. Three TSC with bolt connected were tested and were burnt under temperature 700 °C within 10 minutes. Testing results showed that after 10-minute fire burning, the temperature of central I beam is not of great increased, indicating that the wooden block help transmits heat although the dowel connections which connect steel and wood is directly exposed to the fire. It is also observed that dowel connection and air gaps caused a relatively high percentage of char for the wood surrounding the bolt as 13% of total area. In conclusion, a useful prediction on char depth no more than 5cm could be estimated for 1-hour testing validating the purpose of applying TSC in future.

Cyclic loading behavior of an innovative semi-rigid connection for engineered bamboo-steel hybrid frames

This paper presents an innovative semi-rigid connection for bamboo-steel hybrid moment frames that comprise engineered bamboo beams and steel columns. The connection incorporates a steel hinge and two steel brackets to carry shear force and moment at the end of the beam, respectively. The bracket consists of two segments-a joint segment connected to beam and an energy dissipation panel (EDP) connected to a column via a base panel. In this way, the connection not only serves as a frame joint, but also as an energy dissipation device. Cyclic loading tests were carried out on 9 connections with various EDP length-to-thickness ratios to investigate their failure mode and hysteresis behavior. It was found that by proper design, damage of the frame can be restricted to the EDP while other parts of the frame are virtually free of damage. Hysteresis loops for the connection exhibit less pinching than dowel or bolt type connections. The connection has adequate initial stiffness, strength and ductility to meet structural design requirements. A simplified formula to predict the load-carrying capacity of the connection was developed based on the experimental and numerical results. Good agreement was achieved between the results of calculation and experiment. Recommendations are made for the design of the proposed semi-rigid bamboo-steel hybrid connection.

Investigation of Grouted Dowel Connections for Precast Wall Construction

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Load-Carrying Capacity and Stiffness of Softwood Wooden Dowel Connections

ABSTRACT Historically, wooden peg connections have been widely used in timber joints, particularly during the Middle Ages, and the use of these wooden connections is becoming popular again. In this article, an experimental investigation of seven different combinations of pegged connection parameters is presented. Embedment, single-shear, and double-shear tests of pine peg connections were loaded parallel and perpendicular to the grain under monotonic static compressive loads. Pegs of 10, 15, and 20 mm diameters were tested in three different shapes: straight cylindrical, straight traditional, and conical traditional. All peg shapes exhibited similar maximum loads, but straight traditional pegs exhibited greater stiffness than cylindrical pegs due to the tight fit of the peg. The ultimate load capacities of the straight traditional and cylindrical peg connections were then compared to a model based on Johansen’s theory of timber connections and were accurately predicted in both single and double shear.

DEVELOPMENT AND IMPROVEMENT OF BEAM STRUCTURES ON THE BASIS OF COMPOSITE LOGS’ GIRDERS

Introduction. Experience in the design and construction of beam structures of wooden bridges with composite girders indicates the possibility of increasing the bearing capacity and the length of the overlapped spans.Materials and methods. The most rational load-bearing elements of composite girders can serve as the logs edged on two edges with the diameter of 28 to 32 cm with the maximum use of the most durable layers of sapwood and dowel connections of steel plates with blind cylindrical nags.Results. In contrast to the compounds of composite girders on lamellar nails, the proposed connection greatly simplifies the process of making the composite girders. Such connection also allows using the logging along the length, combining into three or four tiers and increasing the length of the span.Discussion and conclusion. The proposed solutions increase the load-bearing capacity of composite girders and allow them to be used in the structures of wooden bridges under modern automotive loads. Moreover, the calculation method of composite girders on the basis of the method of forces and discrete placement in the beams between the logs of concentrated elastic-datum shear bonds is developed.

Behaviour and push-out test of concrete dowel connectors for longitudinal shear in shallow-hollow composite beams

The shear transferring mechanisms of shallow-hollow composite beams with concrete slab cast in place are different with conventional headed shear studs and have not been investigated previously. In this study, the behavior and push-out test of concrete dowel connectors for longitudinal shear in shallow-hollow composite beams are described. The theory prediction for concrete dowel connectors without tie-bars adopted in this study was based on EN 1992-1-1 and EN 1994-1-1. Push-out tests of three specimens were conducted and the results were compared with theory prediction and published formula to identify longitudinal shear resistance. The failure of specimens and the ultimate failure load values of push-out test were proved that the behavior of concrete dowel in shallow-hollow composite beams was not under pure shear stress.
 Keywords: steel-concrete composite beam; shallow-hollow composite beam; concrete dowel connectors; longitudinal shear resistance; shallow floor structure.

Modeling of CFRP and Glulam Combined Action

In this paper, the results of the structural analysis of glued laminated timber and its joints in corrosive environment are shown. This paper includes calculation results for dowel connections of wood structures using steel and carbon fibres cylindrical dowel pins in accordance with the applicable regulatory documents by means of finite element analysis in ANSYS software, as well as experimental findings.

Exploratory investigation of grouted bar-in-duct connections under direct tensile load

Grouted dowel connections are widely used to resist tension induced by in-plane straining actions and to provide ductility to precast concrete load bearing wall structures. Yet, such connections have not yet been duly investigated. Current design code and standard provisions treat it similar to a simple bar-in-concrete detail. The present study reports the findings of 22 full-scale tests undertaken to examine the bond behaviour of grouted connections under monotonic tensile loading. The examined test parameters included the bar embedment length, bar material and corrugated duct. Results indicate that grouted connections behave quite differently from the bar-in-concrete model assumed in design codes, primarily due to the confinement mechanism of the duct, which provides restraint to lateral expansion of the grout. Varying the embedment length seemed to affect both the bond stress and slip, but did not influence the failure mechanism of the connections. The experimental results were used to calibrate two well-known bond-slip analytical treatments, predictions of which appear to be in good agreement with experimental results. The experimental and analytical findings provide an enhanced understanding on the behaviour of such connections, highlighting the need for revisions in future relevant design code provisions.

Determination of Initial Stiffness of Timber–Steel Composite (TSC) Beams Based on Experiment and Simulation Modeling

Due to improvements in the use of recyclable materials in construction, timber–steel composite (TSC) beams demonstrate high potential for future construction. In this study, a proposed simulation modeling, which was adopted from the simulation modeling of a timber I-shape composite, was applied to estimate the initial stiffness of TSC beams. The strength of each beam could be determined once the initial stiffness was estimated. In addition, a series of experiments were performed to examine the accuracy of the proposed simulation modeling, including the effects of different shapes of steel members, fasteners, and applying and not applying a dowel connection. The results indicated that the simulation modeling could adequately determine strength at a deflection of 1/360 of the span. The ratio of difference between the experimental results and the simulation modeling results was less than 10% if a dowel connection at the web was applied. However, the ratio of difference reached 26% and 24% in the TSC beams without a dowel connection at the web that were fastened with screws and nails at the flange, respectively, revealing the importance of applying a dowel connection at the web. Moreover, the strength of the TSC beams with a dowel connection at the web that were fastened by screws was approximately 15% higher than that of TSC beams without screw fasteners. In conclusion, the proposed simulation modeling can provide designers with a method for estimating the initial stiffness and strength of TSC beams within a deflection of 1/360 of the span, supporting the future application of TSC beams in construction.

Experimental and analytical study on precast concrete dowel connections under quasi-static loading

To create composite behaviour in precast concrete panel construction, grouted dowel connections are widely used owing to their simplicity and ability to divert damage from panels during excessive deformation. Yet, current design codes treat this connection as a bar-in-concrete idealization, disregarding the sleeve confinement and composite behaviour of the assembly. Moreover, the performance of this connection under cyclic excitation is yet to be explored. In this study, full-scale grouted dowel connection specimens mimicking actual field conditions were tested to failure under quasi-static loading. Experimental findings revealed that, regardless of the strain level, grouted connections consistently failed in a pull-through mode by shearing of grout between the lugs of the bar. For all dowel embedment lengths, the load capacity of connections depended primarily on the connection seams of the sleeve, and not on the hoop strain level developed in it. Measurement of the hoop strain values allowed calibrating the Frictional Model, which yielded satisfactory predictions of the experimental results. An empirical model was developed using the experimental results to capture the grout damage due to cyclic excitation, thus providing a rational and accurate design tool for grouted dowel connections in composite panel precast concrete wall construction.

Dowel connections securing roof-diaphragms to perimeter walls in historic masonry buildings and in-field testing for capacity assessment

In the seismic retrofit of existing masonry constructions, global interventions are often needed to inhibit the onset of local mechanisms and to engage the whole building box-like structural behaviour. Such interventions are represented by perimeter ties and roof and floor diaphragms. This paper considers the roof diaphragm strengthening solution and investigates the use of stud connections securing the roof thin-folded shell to the perimeter walls. Stud connections serve the dual purpose of collecting and transferring the out-of-plane inertia forces of the masonry walls to the roof diaphragm, as well as transferring the diaphragm reaction forces to the shear walls. Specific detailing of the stud connection and the adoption of an improved lime-mortar overlay on the top of the masonry walls are proposed to improve the connection strength; without such improvements, the connection capacity would be jeopardised by the reduced shear resistance of the masonry wall due to the absence of significant vertical confining action at the roof level. The intervention entirely changes the behaviour of the connection and significantly reduces shear stresses on the masonry wall. The structural behaviour of the connection is analysed and discussed. Emphasis is made on the conceptual design of laboratory and in-field test procedures and testing frames in order to replicate the boundary conditions in real applications. In-situ tests may help during the design of the roof thin-folded shell system and allow for the efficiency assessment of the connections prior to the final intervention, thereby proving the actual feasibility of the retrofit solution.

Computational Modeling of Laminated Veneer Bamboo Dowel Connections

Laminated veneer bamboo (LVB) is a relatively new building product made from layers of glued bamboo and used in applications similar to lumber. Few studies exist on its mechanical performance; in particular, its failure behavior in dowel-type connections. This study uses both experimental and numerical methods to shed light on the complex stress state of an LVB dowel connection when progressively loaded in compression parallel to grain. A 2D elastic, plane strain finite element model is developed for a 15.9-mm (5/8-in.)-diameter bolt with a bolt hole size of 17.5 mm (11/16 in.) following the associated ASTM standard for full-hole specimen protocol. Experimental tests are used to validate and calibrate the model. Results show that predominant failure occurs off-center of the bolt contact region where the shear stress-to-strength ratio governs. Tensile stress perpendicular to grain, often the primary cause of wood failure, is found to be an influential secondary cause of failure. In addition, a frictional contact analysis leads to the finding that the coefficient of friction is a key factor in predicting shear stress.

Shear-slip behaviour and ductility of composite dowel connectors with pry-out failure

The flexural strength of steel and concrete composite beams is influenced by both the connectors’ shear capacity and the slip across the steel–concrete interface. However, plastic design strategies commonly used in engineering practice assume a rigid-plastic connector behaviour neglecting the real nonlinear shear-slip characteristic. As to prevent a premature connector failure due to excessive beam end slip, design codes usually allow only ductile shear connectors with a deformation capacity δult of at least 6mm to be used. But, especially for innovative shear connectors like composite dowels, approaches for assessing and describing the nonlinear shear-slip behaviour and deformation capacity are lacking, so far. Therefore, the present paper proposes models for the calculation of the slip capacity and the description of the shear-slip characteristic, considering the composite dowels’ shear capacity and elastic connector stiffness. The proposed models can be used to replace expensive and time-consuming shear tests for the characterization of the composite dowels’ deformation capacity. Furthermore, they allow to define the required material combinations and to carve out the dowels’ geometrical dimensions for a ductile connector behaviour.

Structural dynamics of a dowelled-joist timber floor in the low-frequency range modelled using finite element simulation

This paper concerns the development and validation of Finite Element Methods (FEM) to simulate the dynamic response of a dowelled-joist timber floor. This is a solid floor comprised of timber joists connected using timber dowels with individual assemblies connected using inclined metal screws. The focus is on the structural dynamics in the low-frequency range up to 200Hz which is the relevant range for impact sound insulation and vibration serviceability. Dowel connections between the joists that formed each assembly were modelled using either rigid or spring connectors in the FEM models. The validation against experimental modal analysis showed that both approaches were valid in terms of the eigenfrequencies, Modal Assurance Criterion (MAC) and the spatial-average velocity with point excitation. Whilst the FEM model with spring connectors had a higher number of correlated modes in the MAC analysis, this required removal of many spurious modes before predicting the response. The validated models were used to demonstrate the potential in predicting assessment parameters for vibration serviceability that are contained in EN 1995-1-1 (Eurocode 5). This predictive approach to the evaluation of vibration serviceability has the advantage in that it can be used for non-standard timber floors with non-standard boundary conditions or floor plans.

Experimental and analytical study on grouted duct connections in precast concrete construction

Owing to its forgiving tolerances and eliminating the need for welding, grouted dowel in-conduit connections are widely used for connecting various precast concrete elements, for instance in precast wall construction and bridge bent cap systems. Current design recommendations for such a connection treat it similar to a conventional reinforcing bar-in-concrete and do not account for the restraining effect of the duct. In the present study, a series of experimental and analytical approaches have been adopted to explore the disparity between grouted dowel connections and bar-in-concrete. The experimental program consisted of testing twenty-four pull-out specimens under monotonic loads. The main parameters investigated included the embedment length, concrete compressive strength and corrugated duct. Results from the experimental and analytical procedures showed that grouted dowel in-conduit connections behave markedly different from bars in concrete. Different failure mechanisms occurred in the grouted connections due to the confinement effect of the duct. Moreover, an increase in load carrying capacity and ductility of the connections was observed at all embedment lengths, regardless of the concrete compressive strength. Based on the experimental findings, an analytical model for predicting the embedment length of the connection was derived, calibrated and proven to be more accurate than state-of-the-art design procedures.

Analysis of Wood Structure Connections Using Cylindrical Steel and Carbon Fiber Dowel Pins

In this paper, the results of the statistical analysis of corrosion processes and moisture saturation of glued laminated timber structures and their joints in corrosive environment are shown. This paper includes calculation results for dowel connections of wood structures using steel and carbon fiber reinforced plastic cylindrical dowel pins in accordance with applicable regulatory documents by means of finite element analysis in ANSYS software, as well as experimental findings. Dependence diagrams are shown; comparative analysis of the results obtained is conducted.

Cyclic shear tests on RC precast beam-to-column connections retrofitted with a three-hinged steel device

Recent European earthquakes demonstrated that the seismic response of RC precast structures can be significantly influenced by the connection systems. Moreover, during past seismic events, many failures of the beam-to-column connections occurred due to their inadequate strength under seismic loads. The seismic safety of these connections has a crucial role in the overall seismic capacity of existing precast structures. A new connection system is employed as a retrofitting solution for a damaged beam-to-column connection and its cyclic shear performance is investigated by means of two cyclic shear tests on two different configurations. In both the experimental tests, the results demonstrate an efficient behavior of the retrofitted connections under horizontal cyclic loads. The comparison between the performance of the investigated connection and the response of a typical beam-to-column dowel connection allows to discuss the main critical features of the dowel connection system.

Effect of early-age subfreezing temperature on grouted dowel precast concrete wall connections

During cold weather precast wall construction, in-situ heating of the grout used in grouted dowel connections is usually conducted for short periods of time. Hence, early-age exposure to subfreezing conditions may affect the quality of the grout and subsequently the bond strength of the connection, which can compromise structural integrity. In this study, grout specimens typical of that used in precast wall construction were initially cured at ambient conditions for one day and then placed inside a walk-in environmental chamber at subfreezing temperatures. The hardened grout properties and bond strength of the connection were examined and compared to that of specimens cured at ambient temperature. The compressive strength of the grout was monitored at temperatures of 1°, −10° and −20°C. The effect of subfreezing exposure on the mechanical properties, hydration process and pore size distribution of the grout were examined. It was found that early-age subfreezing curing temperatures reduced the compressive strength of the grout, leading to increased dowel embedment length to achieve bar fracture. The bond strength of the connection remained proportional to the square root of compressive strength, even subsequent to early-age exposure to subfreezing temperature.

Design and Construction of Hybrid Concrete-Masonry Structures Informed by Cyclic Tests

Reinforced concrete buildings with masonry infill are vulnerable in earthquakes primarily because the masonry walls often fail due to out-of-plane forces and can trigger soft-story collapses. In order to prevent these failures, many engineers in the Caribbean have partially reinforced the infill walls and connected them to the reinforced concrete frame. This forms a hybrid concrete-masonry structure. Hybrid concrete-masonry structures have the potential to improve the seismic performance of many structures across the globe, as they are an easy adaptation from traditional unreinforced masonry infill. However, there is little codified guidance for this type of structure, and the influence of the masonry infill and dowel connections on the in-plane behavior of the frame is often neglected. This paper summarizes the current design and construction practices for hybrid concrete-masonry structures and assesses their seismic performance via cyclic tests on full scale test specimens. Based on the results of the experiment, a method is proposed to account for the dowel connections and the partially reinforced infill when designing hybrid concrete-masonry structures in earthquake zones.

Load-to-grain angle dependence of the embedment behavior of dowel-type fasteners in laminated veneer lumber

Load-to-grain angle dependence of the embedment behavior of steel dowels in laminated veneer lumber, as a consequence of the anisotropic material behavior of wood, is experimentally investigated in this study. As a novel issue, in addition to the stress dependence, the displacement path of the dowel depending on the load-to-grain angle, is discussed. Full-hole embedment tests of screw-reinforced LVL specimens up to dowel displacements of two times the dowel diameter and thus, representative for highly ductile dowel connections were conducted. Tests were performed with unconstrained lateral displacement boundary conditions of steel dowels with a diameter of 12mm and 16mm. Surface deformations were monitored with a full-field deformation measurement system. Increasing the load-to-grain angle caused reduced quasi-elastic limits and loading stiffness. However, for load-to-grain angles of 60° and higher, a pronounced displacement-hardening effect, leading to high embedment stresses at large dowel displacements, was observed. For the investigated dowel diameters, surface strains and plastic deformations around the dowel indicate an almost dowel diameter independent load bearing area, which might explain higher nominal embedment stresses and consequently a more pronounced hardening effect of the smaller dowel diameter. Dowel displacements perpendicular to the initial loading direction, i.e., nonlinear displacement paths of the dowel, were related to the anisotropic stiffness of wood and densification effects close to the dowel. The established experimental dataset was compared to current European timber engineering design equations and could serve as input to analytical and numerical models of dowel connections.