تعمیرات پیشگیرانه در اتصالات اتصال جوش در پل های راه آهن فولادی

• A new strengthening method for welded joints in railway bridges was proposed.• Effects of present strengthening method were confirmed by using test results.• Both positive bending moment and negative bending moment were applied in the test.• Effective numerical modeling method for the present method was investigated.• The performance of rubber-latex and rapid hardening concrete was studied.Structural repairing or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges. A strengthening method for welded joints in old steel railway bridges by integrating the rapid hardening concrete, rubber-latex mortar, and reinforcing bars is introduced in this paper. The purpose of the present study is to investigate the mechanical performance of the strengthened connection joints in old steel railway bridges. Depending on the locations of the concrete and possible loading conditions, the joint needs to sustain both negative and positive bending moment, therefore, two experimental plans were employed. The static loading tests on the steel joints before and after strengthening were performed to confirm the effects of the present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and original steel joints. Load versus deflection relationship and strain development process on the web of the joints were measured and compared between the original joints and the strengthened joints. Both experimental and numerical results indicate that the present strengthening method can greatly enhance the stiffness and reduce the stress levels of steel joints, resulting in the extension service life of aged steel railway bridges.

In Japan, the construction of new steel bridges has been decreasing. On the contrary, old bridges have been increasing rapidly, and it has been reported that in 20 years, a half or even more of the existing bridges with a span exceeding 15 m were predicted to be over 50 years old [1]. It was also reported that more than 60% of the railway bridge stock in Europe was over 50 years old and more than 30% was over 100 years old [2]. These bridges are subjected to higher loads and speeds than those for which they were designed. To satisfy the present and future demands, some bridges are in need of strengthening or replacement. Meanwhile, due to their high transport capacity and effective use of energy with lowest damage to the environment, railways are one of the most important means of transportation in the world, in which steel bridges have been widely used. After tens of years' service, many of steel railway bridges become old and need to be strengthened integrally for the whole bridge or repaired locally for certain steel members. Considering the relatively high cost for replacing or strengthening integrally, as well as the great impact on the public transportation, preventive maintenance on the old steel members is an effective way. In recent years, engineers all over the world have been working on repairing or strengthening of old steel railway bridge structures. Wallin et al. [2] investigated two different strengthening methods for a through-girder steel railway bridge (Soderstrom Bridge) in the city of Stockholm, Sweden. Experimental and numerical investigation was performed by Lin et al. [3] and [4] on an old steel railway bridge which had been used for 100 years in Japan. The results demonstrate that the use of rapid hardening concrete, GFRP, and reinforcing bars can effectively improve the fatigue strength, reduce the structural noise, and extend the residual service life of the old railway bridges. Fischer and Lorenz presented a study on a historic steel bridge which served traffic for nearly 100 years in Germany [5]. Linghoff et al. [6] and [7] performed both experimental and numerical studies on steel beams strengthened with CFRP laminate in both the serviceability and ultimate limit states. Harald described strengthening of a continuous steel plate girder bridge built in 1939 by using additional main girders, which were connected by prestressed tension rods for unloading the existing structure [8]. Sugimoto and Ichikawa conducted a study to extend the fatigue life of the railway bridges [9]. From the past experience we can conclude that, it is the common choice for engineers to strengthen the old structures by integrating with new structural members or materials. In the engineering practice, the damage of the steel bridges frequently occurs on the longitudinal and horizontal beam connection joint due to severe corrosion and fatigue. For steel railway bridges subjected to large train impact and vibration, fatigue is more critical than corrosion. Besides, as welded structures have been widely used for railway line including bridges, various fatigue damage problems have been reported. In order to avoid the unrecoverable damage of the railway bridge, high cost of the rail line owners and the great impact on the public transportation, effective preventive maintenance methods on the old steel railway bridges are necessary. On this background, this paper presents a new strengthening method to improve the fatigue performance of the welded joints between longitudinal and horizontal beams in steel railway bridges, as shown in Fig. 1 (a). FRP plates, rubber-latex mortar, rapid hardening concrete, as well as the reinforcing bars are used for preventive maintenance on the joint to enhance the loading capacity as well as the durability of existing steel railway bridges (Fig. 1 (b)).

A strengthening method for connection joints in old steel railway bridges was introduced in this paper. In order to verify the effect of this method, static loading tests were performed on two original steel joints and strengthened joints after integrating with rubber-latex mortar, rapid hardening concrete, and reinforcing bars. Detailed load–deflection response, and strain distribution on the steel joints were reported in this paper. A 3-D nonlinear finite element model was established for simulating the present test specimens. From the present results, the following conclusions deserving priority are made: (1) The present method was proved to be effective for increasing both rigidity and load carrying capacity of the connection joints in old steel railway bridges. Short construction period and easy construction methods also make this method competitive in comparison with other repairing or strengthening methods in the engineering practice. (2) A three dimensional finite element model of strengthened steel joints taking geometric and material nonlinearity into consideration was established to investigate the effects of the present strengthening method. The ultimate load carrying capacity, load–displacement curves and strain development process predicted by FE models agree well with that obtained from the experiments, which demonstrates the accuracy and efficiency of the proposed FE models. (3) The effects of bond strengths on the steel–slab interface were investigated, and load versus displacement curves were given. It can be found that the present strengthening method for steel joints without using shear connectors is effective. The effects of the rubber-latex mortar were also confirmed. (4) The performance of the strengthened joints under combined bending and torsion was investigated by applying the eccentric load on the present numerical models. When subjected to torsional moment, the increase of rigidity of the joint after strengthening was also confirmed in the numerical analysis.