Timber-Concrete Composite Structures For Bridges

Benefits of Timber-Concrete Composite Structures for Bridges

Historically, individuals used to construct their bridges by the use of stones and timber. Nevertheless, there have been developments and improvements in every level and different materials which can improve the resilience of the bridge and other types of construction have been discovered. The use of the concrete and steel has replaced all the materials that were used previously due to the disadvantages of the traditional materials used in the construction. This matter encouraged the growth of the responses that limit the weak point on timber and take the benefits of the long-lasting constituents of it. After that, the structures of timber-concrete composite used on the bridges will display an exceptional ability. This method combines the force in the compression of concrete with the strength of timber in tension which network by making a sufficient connection between the materials. This means that both strength and stiffness of the wood and concrete when combined gives substantial benefits that make the bridge made of those materials to last longer.

The density of the timber-concrete composite is light compared to another composite system since the structure can carry a load three times compared to using timber alone, and more than six times the rigidity of flex. The use of the reinforced systems of concrete has led to low efficiency on the capability of carrying the load and it’s self-weight. As soon as the viable of the motion of the composite completed, the reduction of the sizable deformation and development of the potential of conveying load could be expected in the timber structure assessment. The timber concrete structures are considered to be a good substitute for the constructions of the existing usage in the building of the bridge and their intersection.  

Many people are now using more of their resources in the building work specifically in the industrial sector, and a greater percentage of it goes to the solid wasted. The organizations and firms have adopted the plan of sustainability and improvement of the current structures by upgrading new innovations such as the use of timber-concrete composite structures in the bridges. The deck of timber-concrete is able to withstand the weight by the use of three components which include the structure that conveys shear to the timber-concrete composite, the scheme that connects a slab of RC compression, and the timber beam that function when placed in tension longitudinally.

In the bridge structures of the timber-concrete composite, the concrete placed at the top of the timber functions as a joint resist compression, bending and tension consecutively. There is a connection between the two components that are responsible for the shear.  The whole process and the behavior of the components and all materials during the existence of the bridge result in a complex investigation of long-term. It depends on the timber material that is used in the structure of the bridge (solid non-graded maritime pine, glued laminated and solid non-graded chestnut). The usage of those products in the structure is highly relevant.  The content of the moisture is considered to be dry (10 to 13%) so that it cannot be ranked as the issue to deal with it. The structures will be in good working conditions if pre-planned maintenance takes place and also when some necessary consideration is noted like durability and foundation of the structures (Bakht, 2015).

Comparison of Timber-Concrete Composite Structures to Traditional Materials

Concrete timber composite system is normally composed of the layer of concrete slab that is in the timber ribs stress and compression tension stress which shows that the material’s stiffness and strength are used to the utmost advantages. They are not heavy as compared to other reinforced systems of the concrete since wood has the low density as compared to concrete. The load weight is tripled by the system if the concrete and timber are connected well, the carrying capacity is up to six times the rigidity of the flex of the floor system for the traditional timber. The bridges made of concrete timber are more efficient in term of the load carried per self-weight unit, and also they are very rigid making them strong in the event of earthquakes, and this allows the procedure of the seismic analysis.

The structures are highly dumped and this help in the springiness reduction as well as having good characteristics of the sound insulation. The system of the timber improves the insulation of the noise transmitted through the air and have good performance on fire (Board, 2014). The upper concrete slabs provide a barrier against the propagation of fire that increases the resistance to fire

The timber-concrete composite used in the bridges such as existing concrete and steel instead of the materials that are old leads to the positive outcome like the light weight of the structure and also cost. The deck bridge replacement as reconstruction has displayed that the preliminary cost is approximately one half the RC if the timber deck glued and laminated is used and a lifespan of 50 years. The timber-concrete composite beams have been subjected to the condition of the cyclic moisture and the induced significant deflection of both the beams. The content of the moisture cycles from dry to wet and again to dry and deflection follows a cyclic pattern again (Chen, 2015).

During the test, an increase of the content of moisture and relative humidity is accompanied by the increase in deflection and when the humidity increase the recovery decreases partially. This behavior is found to be the typical response of the bending wood under the conditions of cyclic humidity.  The long-term tests setups start with beams placed on the arrangements directly supported and the extended load applied using the lead bar placed evenly on the top of the beam. The lead bar was manually used on top of the beam (Cobb, 2014). The applied service load is the same as the load that is uniformly distributed. The load applied was about 34% of the ultimate short-term design of the 105 loads expected for the beams.

Structure and Function of Timber-Concrete Composite Bridges

The instantaneous mid-span deflection after the load application was 6.5mm and then 6.2 for the second time.  The dissimilar between the instantaneous deflections can be slight because of the spacing variation of the lead bar along the beam length and individual variation in mass of the lead bar. The developed stress because of the bending of the cross-section of the beam composite immediately after the application of the load were, 2.6 MPa, 2.2 MPa, 3.5MPa, and 4.6 MPa on the top flange, webtop, web bottom, and the flange bottom. The range of the stress was 5 to 11% of the capacities design of members and obtained using the transformed method section of a fully composite part for a duration of 800 days (Council, 2015).

The configuration of the joint pedestrian bridge was established, and the tests performed in both uncontrolled and controlled climate. The applied load to the joint was approximately 30% of the transitory load caring boundary of every setup joint. The period was also short in terms of the years. The lifespan of the bridge should be the time frame in which it is expected to last.  In order to handle this issue, the resultant values were estimated and plotted to be the 50 years joint creep. The utilization of the joint configuration was meant to scheme the real performance. The dowels utilized are ten and eight millimeters smooth of standard strength concrete. The timber utilized as the base materials was glued laminated timber (E, 2014).

The achievement of the stiffness and high bending of the timber composite concrete is important for the construction of long-term concrete timber. The following are the objectives of the journal paper:

• To investigate the performance of the timber and concrete composition
• To evaluate the short and long-term deflection
• To know if the composite will be feasible or not

In this journal paper, the following are the research questions that will help in the determining and accomplish the research objectives:

• What are the timber-concrete composite structures?
• What is the long-term performance of the beams of timber-concrete composite and the creep influence expected?
• What is the long-term performance of the pedestrian bridge made of the timber and concrete?
• How conditions of the environment like temperature and moisture affect the concrete timber composite in a bridge?
• Is it feasible to create the timber and concrete as the alternative in the structure construction over the concrete and steel?
• What is the optimum solution concerning the different types of the reliability and cost?

This section explains the methods that were employed in this research on the high performance of the pedestrian bridge of timber and concrete. After interviewing different people, the researcher will be able to find the different suggestion about the performance of the pedestrian bridge made of concrete timber. The methodology that will be used in this research depends on the respondent age, education and company ranks. The research should be performed in a good manner so that all the objectives are met and can only be possible when the effective methodology as well as collecting and analyzing data properly. The interviews were based purely on the personal observation and structured questions. The objective is to uncover the feeling, emotions and views of the participants on the performance of the pedestrian bridge. Personal observation and discussion gave the opportunities for the interviewer and interviewee to establish interview directly. The targeted age group is 20 to 60 years (Engineering, 2014).

Maintenance and Durability Considerations for Timber-Concrete Composite Bridges

The assumptions made are: that there is a relationship between the mechanics of the creep and the performance of long-term of the timber-concrete composite beam. Secondly, there exists the influence from the thermal condition of the humidity on the deflection, stresses of a timber-concrete composite bridge, and the influence on the reaction triggered by the timber composite’s stiffness and the concrete (Engineers, 2012).

The research was done within the construction industry, ministry of transport, and pedestrians. The research study took about three weeks. The collection of data was through the interviews, email, phones and social media also plays a very important role because it was viewed as the valid information of the research. Since people are busy at work during weekdays and daytime, the interviews sessions were timed on the weekends that given the maximum time. The interview session lasted between 40 to 55 minutes. Also, the session coincided with the festive seasons when the people were happy and eager to respond to the researcher questions. The gathered data will be geared towards the studies objectives aimed to help the researcher in the conclusion (Establishment, 2014).

The interviews were conducted in the following areas:

Construction industry: During the visit to various construction industries that construct bridges, the managing directors and CEOs were asked some of the questions by the researcher since they are the ones doing the job, they can have detailed information. The following are some of the questions that they were asked:

• What is the long-term performance of the pedestrian bridge made of the timber-concrete composite?
• What are some of the environmental conditions that affect the bridge mage of timber-concrete composite and how?
• It is feasible to create the concrete and timber as an alternative
• What is the short and long-term deflection?
• How can you compare the structures made of the timber concrete with the ones made of old materials?
• What are some of advantages and disadvantages of the pedestrian bridge made of timber-concrete composite

Ministry of transport: Since the constructions cannot happen when the ministry of transport is not consulted, they were also interviews for the detailed information. The following are some of the questions that they were asked:

• What is the long-term performance of the pedestrian bridge made of the timber-concrete composite?
• What are the environmental conditions that affect the pedestrian bridge and how?
• How can you compare the performance of the bridge made of timber-concrete and others that are made by other materials?
• What are some of the disadvantages and advantages of the pedestrian bridge?

Pedestrians: pedestrians were also interviewed because they ate the ones using the bridge. The following are the questions that they were asked:

• What are your views about the performance of the pedestrian bridge made of timber and concrete?
• What are the advantages and disadvantages of the bridge made of timber and concrete?
• State some of the factors that affect the pedestrian bridge made of timber and concrete?
• What are some of the factors that must be considered before construction so that a long performance bridge is constructed?

In this section, the assessment will be done concerning the timber-concrete composite and its creep relation. The creep of the timber-concrete composite beam will affect the bridge work. In the experiment, the joint configuration approximately seven was established and the examination occurred in both uncontrolled in addition to controlled weather. The applied load joint was approximately 30% of the transitory limit of transporting a load of every distinctive set up (Engineers, 2012). The time frame of the bridges was 50 years.

 Table 1 above show the values of the creep that was calculated in uncontrolled and controlled climatic conditions

In the modelling of the creep, the study of the behavior of the long-term timber and concrete has the limit of time hence an important issue to develop the creep factors. The effects of the stress plus deflection were examined and measured on the basis of prolonged duration. The assessment was made with three different timbers longitudinal and vertical as well as the cross-sectional area was enclosed by the coating of the sheet known as OSB. RC fibre included the specimen of the beam and the shear linking was mounted by use of the screws. Every screw was placed at 45 degrees to the cross-sectional area.  The condition of the outdoor deck bridge was humidity and the environmental temperature (Establishment, 2014).

Testing and Performance of Timber-Concrete Composite Beams

The test of the creep gotten during the performance of the research conforms to the data from the experiment. It was realized that the creep value that was obtained for 10m was small for uncontrolled and controlled conditions of the weather. This is because of the time that was very short when the test was applied. Through estimation, the creep value on the prolonged duration basis will be advanced for the controlled climate. It is observed that it affects the variation of the moisture concerning the test of the condition of the weather when controlled. When compared to other joints, the outcome shows a low value of 10mm (E, 2014).

Figure 1 above shows the time curve of the creep test for 8mm

Figure 2 above shows the time cure of the creep for the test for 10mm

The specimen showed similar time-dependent performance in the relation to the deflection examination with the humidity and thermal variations. The high sensitivity of the beams of the timber-concrete composite on the situation of the environment was also noted. There was a relation on the deflections to the high temperature where the argumentation with the progression of time was shown. The changes in the environment can cause additional values of the deflection to the structure of the bridge (Board, 2014).

The figure 3 below shows the cross section parameters of the geometry

Figure 4 below shows the outcome of the long-term test

The timber-concrete composite structures represent a technique utilized in the construction of new buildings or stiffness and strength improvement of the existing structures of traditional timber. The prolonged performance of the timber composite concrete is characterized by the interaction that is the complex between the components of the system like timber, concrete and the systems for connecting. The woods structure’s long-term behavior depends on many issues like the level of the stress, content of temperature and moisture.  The primary long parameter design for the timber-concrete composite is the deflection that is linked to the creep (Federation, 2015).

The variation rate exposing timber concrete bridge to any span of the lifecycle have mentioned the impact on the deflection, with many variations in the composition of the moisture giving rise to many creeps under the load that is bending. A fast reaction to the change in humidity is mentioned when there is the change in the cycle of humidity to dry from wet. Throughout this change, the moisture escapes at a rapid rate from the surface than from the LVL’s middle cross section, resulting in a reaction that is fast from the beam. In the dry seasons, the deflection was initially increased faster and then after some time. There was a prolonged level when the maintenance of the environment on the seasons of dry plus displaying the flattening trend at the same region (Khan, 2015).

Research Methods for Evaluating Timber-Concrete Composite Bridge Performance

It is important to control the deflection in timber of the long-term significantly by surface treatment application against moisture. The long-term performance of the bridge of timber and concrete depends on the concrete, creep swelling and shrinkage effects in the timber and connections of creep affect the strength of the long-term, deflection and stiffness behavior of the timber concrete. The variation of the moisture is the reason why the creep is in the timber. Factors like loading type, surface properties, size, and the environmental length cycle affect the long-term behavior of the timber concrete bridge indirectly (L, 2014).

The behavior of the timber concrete bridge depends on the time needed for the prediction of the long-term deflection accurately. The test of long-term need more preparations and is very expensive since requiring the validation of the procedures of the approximate design and to calibrate the existing numerical and analytical models. The test that was conducted in the uncontrolled weather conditions for 133 days indicates the increased content of the moisture since the fresh concrete bleeding is not the issue for the wood deck durability and the construction type does not significantly affect the structural performance. The use of the pre-cambering and propping the timber before it is concreted and use of the concrete of low shrinkage or the precast of the concrete slabs for the application of the span term to reduce the deflection of long-term was recommended (U.S. Department of Commerce, 2015).

The experimental results for a duration of eight hundred days show the tendency that is generally towards the creeps and curves flattening with a slow rate of the creep increase for both the time and beam.  The beams deflected more than 3 times their sudden deflection. Based on the experimental findings, and considering the deflection increase expected over time, it can be suggested that the general creep factor of three foes the timber composite beams in the conditions of the environment. According to the Eurocode 5, the creep wood exhibits the behavior of the linear with respect to stress level and stress of about 40 to 50 % of the strength of short-term in the persistent environmental conditions as reported in bending, tension and the compression (Publications, 2014).

In the creep, the woods of nonlinear starts at around 10 to 20 % of the final stress in the compression and around 20 to 30% of the ultimate stress in the bending and tension. With normally larger the deformation of the creep under the load compressed under the load tension. The swelling and the shrinkage is because of the changes in moisture that also affects the deformation which afterwards affects the modulus of the elasticity. For the results concerning the glued laminated timber bridge, the findings of the creep test when the research was carried out complies with the experimental results (Engineering, 2014).

It was noted that the value of the creep that was obtained was too small for both uncontrolled and the controlled conditions. This can be due to the short period that the test was done. Through the forecast, the worth of the creep stretched was higher for the climate conditions uncontrolled since it shows that it depends only on the changes in the moisture. In the experiment of the controlled condition of the weather, the results show low value as compared to the joints. There was the high sensitivity of the beam of the timber concrete bridge to the situation of the environment. There is also a relation between high temperature and the humidity to the deflection.  The values of the environment can result in the deflection of the structure of the bridge (Merritt, 2011).

Conclusion

From the above results and analysis, the use of the timber concrete bridges deck is the feasible choice when considering the criteria of working and sustainability. Timber-concrete composite bridges are better and perform well than other types. It is critical to set the investigations of the life cycle such as monetary, ecological and measurements of social-cultural notwithstanding the point that there is no customary methodology for the supportability of indispensable evaluation of the parts. This journal paper also shows that the span of the timber is a great choice for the supplanting steel span or the old cement with replacing the projections and old establishment. Good choice for the bridge can be met when considering the construction and the favourable conditions for the lightweight for the acceleration the time frame development.

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