the numerical solution of the bolted connection with the low-quality injected bolts

Proceedings of the 9th International Conference on

New Trends in Statics and Dynamics of Buildings October 20-21, 2011 Bratislava, Slovakia

Faculty of Civil Engineering STU Bratislava Slovak Society of Mechanics SAS

THE NUMERICAL SOLUTION OF THE BOLTED CONNECTION

WITH THE LOW-QUALITY INJECTED BOLTS

Ing. Ján Kortiš, PhD.1

Abstract

Many failures have showed during the usage of the old riveted steel bridges and the serviceability is limited by

the quality of the reconstruction. The riveted connections are often the sources of the failures. The injection bolts

are applied to repair old riveted connections if the repairing by using the rivets would be difficult because the

experienced riveters are not available. The injection bolts could be also used for new structures hence the resin

prevents the bolts from extending of the corrosion process. The quality of bolted connection with injected bolts

depends on the parameters of the resins and the realization of the injection. If the injection is not realized

correctly the problems with high local stress could be a source of the potential failures. This could be problem

primarily in the riveted connections where the injected bolts are replaced damaged rivets. The failures of the

rivets could be cause by the different stiffness of rivets and injected bolts.

1 INTRODUCTION

The injected bolts are installed into holes which are 2 to 3 mm bigger than the nominal diameters of the bolts. The cavity between bolt and the wall of the hole have to be completely filled up with two component resin. The resin is injected trough a small hole in the head of the bolt. The bolt connection with using the injected bolts is assumed to be slip resistant after injection and complete curing of the resin. This gives them possibility to apply them instead of rivets or fitted bolts in shear connections especially in cases when the technology for rivets connection is not available or the cheapest and simple solution is required. But securing the quality of the fulfilling of the cavity is very difficult and there are not any applicable methods to verify it. It can be a problem if the injection bolts are used to replace the damaged rivets and their presence in riveted connection could change the loading of the existed rivets. The numerical model of the riveted connection with two rivets was created to evaluate the development of the stress in one of them and the injected bolt was used to replace the next one. The quality of injection in the model is changed and cavity is only half-filled with resin. The models of connections with two rivets, with one rivet and injected bolt and with one rivet and the low-quality injected bolt were compared and evaluated by the effective stress in the first rivet. The geometry of the model and the results are presented in the following parts of this article.

1 Ing. Ján Kortiš, PhD., Department of structural mechanic, Faculty of civil engineering, University of Žilina, Univerzitná 8215/1, 010 26 Žilina, phone: ++421 41 513 5616 , e-mail: [email protected]

9th International Conference on New Trends in Statics and Dynamics of Buildings October 2011, Bratislava

2 THE ASSUMPTION OF THE SHEAR CONNECTION WITH INJECTED BOLTS

We assumed installation of the non-preloaded injected bolts which transfer the load only by shearing and bearing. This is useful if the friction coefficient of the contact surfaces is very low or the determination of the friction is very difficult. This is a problem of the old riveted bridges where the contact surfaces of the steel plates could be corroded from the exposure to moisture in the air or the anti-corrosion coating like paint was applied on the surfaces. The slip factor for this connection is assumed on the same value as the fitted bolts. This assumption is right if the reasonable thicknesses of the steel plates are used for connection and the bolt’s length does not exceed the required value otherwise the loading could not be assumed as equally redistribute on the bolt. The required values and restrictions are prescribed in European recommendations for bolted connections with injection bolts [1]. These recommendations were used to define the dimensions of the model’s parts.

Fig. 1. The example of the injected bolt installed in the shear connection

The shear load has not exceed the design shear resistance of the bolts and bearing resistance of the resin. The bearing resistance of the resin is defined by serviceability limit state:

Fb1Rd,ult,resin�1,2. ks. d. t. β. fb,resin

γMs,ser

(1)

where the fb,resin is the long duration bearing resistance where the displacement due to creep is not greater than 0,3 mm. There is prescribed that the bearing load of the resin may not exceed 130 N/mm2 which is design bearing resistance value for widely used resin ARALDITE SW404 with HY 2404 hardener. The next material characteristics used to define the material of the resin for the numerical model are: after cure for 7days at room temperature or 14 hours at 40 °C Elastic modulus 4,5 – 5,0 GPa Density at 25°C 1600 kg/m3 Poisson ratio 0,35 The bearing resistance of the resin was used to define the loading force on the steel plate for evaluation of the influence on the shear connection with rivets and injected bolt. This loading force was the peak value and it was assumed that there could not be the stress which may damage the resin. The design shear resistance of the bolts and rivets were not considered because the final behavior of the connection was not known before the evaluation of the results. The material of the steel plates, the rivets and the bolts used in model was defined as an elastic isotropic material and the material characteristics define the behavior of the convenient steel material. It was not analyzed plastic deformations to assure the stability of the solution because there may be some problems with convergence and the main goal of this work was only to find out the influence of the injected bolts installed in the rivet connection.

chamfered washer

resin

air escape groove

injection hole


The geometry of the numerical model was made as a shearing connection with one rivet and one injected bolt. The injected bolt was changed for rivets and the low-quality injected bolt and it gives opportunity to compare the results loading of the examined rivet. Te dimensions of the steel plates are showed on the next figure. There was used a rivet which fulfilled the hole and bolt which diameter was 2 mm smaller than the diameter of the hole. The cavity was fulfilled with resin at the beginning and then was filled up only the half space of the cavity. This simulated the low-quality injected bolt which could caused if the bolt is injected from the lower part and there is not given enough amount of the resin. The upper part of the cavity was free.

Fig. 2. The dimensions of the modeled connection

3 THE DESCRIPTION OF THE NUMERICAL MODEL

Geometry of the model was imported from CAD software and improved to generate good mesh. The 3D solid elements with eight nodes were used to generate mesh. The mesh of the rivet and bolt with resin was created by revolution of the 2D elements with four nodes. This technique gives better quality of the mesh, which is difficult to secure on the curved or circular contact surfaces. The nodes generated on the surfaces of the rivet and bolt did not penetrate the target surface of the holes and the initial cavity between contact surfaces was only 0,01 mm. The same quality of the mesh for rivet and bolt prevented before later activation of the rivet or bolt which may lead to wrong results. The mesh is denser in places of the contact surfaces.

Fig. 3. Numerical model of the shearing connection with two rivets

analysed rivet


The zero displacement for all directions was defined on the left surface of the upper and lower steel plate. The loading which value was explained in the previous chapter was applied on the right surface of the middle steel plate. The zero displacement in form of loading was defined on the heads of the rivet and bolt and the displacement with low value was defined on the left surface of the middle steel plate during the first twenty time steps. These displacements gave conditions to ensure convergence of the solution. The displacement was changed to force loading during the twenty time step. The values of the forces were zero at the end of the solution, because this loading is not at the real shear connection. These loading conditions were leaded by the time functions and special facilities the software offered to change the prescribed loading to force loading which replace the reactions which were in places with prescribed displacement.

Fig. 4. Boundary conditions and loading of the model during the last time step

4 THE EVALUATION OF THE RESULTS

Four models were created to evaluate of the influence on the connection with one rivet and different kind of the second connecting element. The maximal values of the effective stress were on the rivet if the next hole was free. If the rivet was inserted in the hole the value of the effective stress has only half-rate of the previous value. Usage of the fulfilled injected bolt lowers the effective stress but not with the same rate as the rivet. It means that the elastic properties of the resin cause that the bolt was loaded with low value so the rivet has to transfer higher loading.

Number of

the model Description

Max value of the

efective stress on

the rivet [Mpa]

Comparison of the values

of the efective stress

[%]

1 one rivet 551,30 100 ,00 2 two rivets 241,10 43,73

3 one rivet and one fulfilled

injected bolt 352,70 63,97

4 One rivet and one half-filled

injected bolt 811,10 147,12

Tab. 1. Comparison of the values of efective stress on the rivet

The worst alternative is the using of the half-filled injected bolt where the effective stress is higher than the effective stress on the one rivet connection. This was caused by the non-symmetry behavior of the connection where the lower connection between stress plates has higher stiffness than the upper because the cavity between bolt and hole caused that the bolt is not activated.


one rivet and one fulfilled bolt two rivets

one rivet and one half-filled bolt one rivet

Fig. 5. Effective stress on the rivet

The distribution of the effective stress is showed on the previous figure. The highest values are in the places where the contact is defined between two steel plates. The effective stress is composed not only from shear stress but the tension stress in the direction parallel to axis of the rivet too. This is caused by tendency of the plates to shift off so the values could change if the distance between rivets or injected bolts is different and if the first or the second rivet or bolt is evaluated. But the differences are not very large. The differences could be larger if the length of the rivet and bolt has been higher. The effective stress is higher than the elastic limit and it should be solve with a non-linear material characteristics. However, the comparison of the influence on using injected bolts to replace the rivet is better if the elastic model of the material is used. The boundary conditions change the values of the effective stress so the specific behavior of the connection could happen if the different boundary condition has been applied.


5 CONCLUSION

The assumption that the behavior of connection with injection bolts is the same as the behavior of the fitted bolts could not be right if it was used in rivets connection because the deformation of the injected bolt is higher thanks to the low-stiffness of the resin . The resin prevents from sudden slip in connections with preloaded bolts and the internal corrosion is avoided thanks resin which fulfills the internal cavity between bolt and wall of the hole. This technology may used if the riveters are not available but it is important to secure the condition of the installation. The quality of the injection has big influence on the loading of the others construction parts in the connections like rivets.

REFERENCES

[1] ECCS, (1994) European recommendations for bolted connections with injection bolts. ECCS publication No. 79 Brussels. [2] G. Sedlacek, M. Paschen, Injection bolts to repair old bridges, A.M. Gresnigt, Delft University of Technology, The Netherland, http://www.epicuro.co.uk/uploads/349.pdf [3] A.M.P. de Jesus, J.F.N. da Silva, M.V. Figueiredo, A.S. Ribeiro, A.A.Fernandes, J.A.F.O. Correia, A.L.L. da Silva, J.M.C. Maeiro, Fatigue behavior of resin-injected bolts: an experimental approach, Iberian Conference on Fracture and Structural Integrity 2000, march 17-19, 2010, FEUP, Portugal

the numerical solution of the bolted connection with the low-quality injected bolts

Documents