The ultimate goal of every research is not the objectivity, but the truth. We search for knowledge or perform a systematic investigation to establish the facts. The primary purpose for our applied research is towards discovering, interpreting, and developing methods and systems for the advancement of the knowledge of mankind on scientific matters of our world and the universe.
Perhaps in a research, it may take three months to write the objectives; three minutes to conceive it and all our life to collect the data in it.
Repair and Strengthening
The recent garment factory-building collapses in Bangladesh have raised awareness of the necessity of strengthening existing factory buildings to achieve building safety compliance. In this context, structurally deficient columns, as one of the most critical members in a structure, are a major focus in strengthening noncompliant buildings.
Furthermore, in flexural retrofitting, the application of externally-bonded carbon-fibre-reinforced polymer (CFRP) pultruded plates has emerged as a useful technique (externally bonded steel plates, the forerunner of CFRP plates) for enhancing the flexural capacity of reinforced-concrete (RC) beams. In such applications, the plates, which are externally bonded to the unconfined cover concrete at the tension face, often debond prematurely.
Two recent successive publications from the research Group of Prof. Amin are expected to be the key fundamental observations towards rationalizing the strengthening techniques for axial and flexural members. Estimation of design parameters for axial strengthening will be useful, particularly for Bangladesh that uses dilatable low strength concretes. The identification of design parameters in prevention of debonding in flexural strengthening will be useful for future development of design codes globally.
Hasnat, A., Islam, M. M., & Amin, A. F. M. S. (2015) | Islam, M. M., Choudhury, M. S. I., & Amin, A.F.M.S. (2015) | Islam, M. M., Choudhury, M. S. I., Abdulla, M., & Amin, A. F. M. S., (2011) | Hasnat, A., Islam, M. M., & Amin, A. F. M. S., (2011) | Amanat, K.M., Amin, A.F.M.S., Hossain, T.R., Kabir, A., Rouf, M.A., (2010)
The Ganges, the Brahmaputra-Jamuna, the Surma-Meghna and the Padma and their numerous tributaries and distributaries are the arteries of the drainage system for the country. In such a geological formation, the construction and maintenance of an uninterrupted road-rail, telecommunication and power transmission network across the country poses to be the biggest challenge for the civil engineers. In this scenario, Steel bridges, e.g. Hardinge Bridge, Bhairab Bridge, Teesta Bridge, Keen Bridge are the examples of steel bridges, a few of those are serving us near about last 100 years. However, to maintain these bridges, the maintenance engineers need to combat with corrosion that is mostly resisted with painting and re-painting round the year.
Until the mid- to late-1970s around the world, virtually all steel bridges were protected from corrosion by multiple thin coats of lead- and chromate-containing alkyd paints applied directly over mill scale on the formed steel. The paint system commonly used for steel bridge members contains chromium and lead and can no longer be used because of the effects it has on humans and the environment. Furthermore, the telecommunication and power transmission backbone of Bangladesh depends largely on steel towers and monopoles that are mostly galvanized to resist corrosion. However, hot deep galvanization process restricts the maximum weight of steel members, therefore most of the galvanized bridges and towers are of small members connected through joints.
To remove the above difficulties, weathering steel, a new type of material that exploits the beneficial properties of corrosion has been developed in the past. This material has been proved successful in many countries around the world and now constitutes about 40% of total consumption of structural steel over the world. This type of high-performance and high strength weathering steel does not require painting/galvanization for corrosion protection. Introduction of this new range of steel has drastically increased the number of steel bridges being built through the world. Initial cost of weathering steel is almost similar to ordinary steel but the maintenance cost incurred for weathering steel is significantly less from that of ordinary steel. Life cycle cost ordinary steel is now estimated to be 4 times than that of weathering steel.
The absence of any first hand field data for Bangladesh on these aspects has certainly restricted the use of this new material. The proposed research is motivated to examine the feasibility of the use of weathering steel in Bangladesh, where the climatic conditions are hot, humid but presumed to be low in airborne salinity content.
Use of weathering steel reduces a significant amount of maintenance (in other turn, the life cycle cost) and increases lifetime of the structures. However, it has certain limits of applicability in regard to environmental conditions. Salinity is the major known limiting factor for its use and durability. Airborne salt affects inherent the mechanism of corrosion resistance of weathering steel and makes it ineffective. However, at present no information is available either on the airborne salt content or the weight loss of any type of steel due to corrosion in any location of Bangladesh. The aims of this research are as follows:
- – To collect first hand data for airborne salt at different geographical locations of the country.
- – To expose different grades of steel specimens including weathering steels to the actual environmental conditions and thereby to make direct comparisons between different grades of steel.
- – Attempts are being made to make a comparative assessment of life cycle costs for different grades of ordinary steel and weathering steels at different geographical and climatological locations of Bangladesh.
After successful completion of this study, the results and conclusions will be presented in seminar and published in local and international journal/proceedings to form a basis for forming the future design approach in the country with this promising material. The outcome of the study will also be valuable to rationalize the existing corrosion protection approaches in bridges and exposed structural members made of ordinary steel. The data gathered from the study will also be useful for developing corrosion models across the country for different climatic conditions and its expected change over the time.
Constitutive Models for Rubbers
We study the emotions of materials. How does a material respond when subjected to an excitation? The response can depend on the history of excitation. On the other hand, the excitation can be stress or strain or even a change of thermodynamic temperature. Perhaps, under such excitations, the microstructure of the material deforms or undergoes though a metamorphosis process. We attempt to study the phenomena that take place within the finite domain of microstructure.
Material behavior of rubber seldom follows the classical elasticity theories. It is sensitive to rate of excitation and history. We attempt to predict the short term and long term behavior of rubbers under large deformation, high strain rate and consider geometric and material nonlinearities. What do you think about the other case, when the deformation is small, strain rate is small or the behaviors are linear? We attempt to write equations that are meant to express all such emotions of rubber. Perhaps these are the generalizations, away from the classical theories and the one can try to describe the simpler cases through simplifications of all such derivations. We consult the theories of continuum mechanics, thermodynamics, thermophysics and a bit chemistry as well. Our domain of consideration is a bit vast and wide.
The outcomes from such research do have applications in different field of engineering. In civil engineering, it is important to design the base isolation bearings for earthquake protection of bridges and buildings, traditional bridge bearings and tunnel linings. In the semiconductor industry, we need to design the seals and gaskets. These may be quite expensive as along as the adopted production technology is expensive. In aerospace and automotive industry, vibroacoustics issues need to be addressed adequately. In biomedical engineering, how do you think about the advantages of a shape memory polymer stent for treating the coronary heart disease? The constitutive equations working behind are the key to offer you a better performance.
Amin, A. F. M. S., Bhuiyan, A. R., Hossain, T., & Okui, Y. (2014) | Razzaq, M. K., Okui, Y., Bhuiyan, A. R., Amin, A., Mitamura, H., & Imai, T., (2012) | Amin, A.F.M.S., Lion, A., Hofer, P., (2010) | Amin, A.F.M.S., Lion, A., Sekita, S., Okui, Y., (2006a) | Amin, A.F.M.S., Wiraguna, S.I., Bhuiyan, A.R., Okui, Y. (2006b) | Amin, A.F.M.S., Alam, M.S., Okui, Y. (2003) | Amin, A.F.M.S., Alam, M.S. and Okui, Y. (2002)
FE Implementation of Constitutive Models
The constitutive models express the emotions of a material when subjected to an excitation. However, to harness the benefits of such models, we need to use a numerical method, e.g. finite element method so that a boundary value problem can be solved. We try to determine a computational strategy for implementing a constitutive model in a general purpose finite element code so that the emotions expressed by a constitutive model can be translated and adopted in a real day analysis situation.
In case of rubber, the challenge lies with the dealing of not only the nonlinearities but also the incompressibility feature that does exist in every rubberlike material. In a complex situation, how do you think about simulating the response when the structure is subjected to a stochastic excitation, e.g. an earthquake or the flow of blood within the shape-memory polymer stent implanted in the heart? We attempt to take the challenge.
Base Isolation Bearings & Expansion Joints
Bearings and Expansion Joints
Bridge superstructures have to be designed to permit thermal and live load strains to occur without unintended restraints. Bridge bearings have to transfer forces from the superstructure to the substructure, allowing all movements in directions designed by the designer. The two functions – transfer the loads and allow the movements only in the required directions for a long service time with little maintenance are not easy to fulfill. Different bearings for different purposes and requirements have been developed so, that the bridge designer can choose the most suitable one.
By the movement of a bridge, gaps are necessary between superstructure and substructure. Expansion joints fill the gaps, allowing traffic loads to be carried and allowing all expected displacements with low resistance. Expansion joints should provide a smooth transition, avoid noise emission as far as possible and withstand all mechanical actions and chemical attacks (de-icing) for a long time. A simple exchange of all wearing parts and the entire expansion joints should be possible.
In BUET, we study the subject to develop local expertise for quality control and quality assurance of rubber bearings and expansion joints. Maintenance, durability, life cycle analysis, replacement techniques of joints and bearings are also the points interests to address.
Base Isolation Bearings
Base isolation bearings have designed flexibility under lateral load and stiffness under vertical load. The damping characteristics in the bearings are ensured by use of either lead-plugs or high damping rubbers. We study the hysteretic behavior of high damping rubber bearings (HDRB) and lead rubber bearings (LRB) to design the hysteresis behavior and incorporation in the earthquake resistant design of structures. Not to mention, such research and development activities are closely related with the fundamental mechanics of rubber and its constitutive behavior. See further details in the section: Constitutive Model for Rubber.
FE Modeling of Shells
Shell is one of the strongest structures available in the nature. The nature generally relies on shell structures to protect the eggs and seeds for reproduction. The shape of the natural shells are optimized to carry the expected loads and mechanisms. Most bird eggs having an oval shape are one end rounded and the other more pointed. Load carrying capacity of an egg in the direction of major axis is much higher than in the direction of minor axis.
How do we think about a coconut falling from the tree to a sandy beach? Or the shell (hull) of an ocean going ship? Or the fuselage of an aircraft flying at a high altitude?
Being motivated from nature, engineers adopted shell as one of the basic structural forms for long span structures. The architectural elegance is maintained together with the material economy and enhanced load carrying capacity.
It is a challenge for us to analyze the shell structures. Shell elements in finite element technique can give you a reasonable result but perhaps a rational analysis can be performed if we can also consider the geometric and material nonlinearities. In BUET, we have mastered the method of analysis based on finite elements and developed design principles for helicoidal shells, paraboloids and hyperboloids.
Curing Behavior of Concrete
Concrete gains strength through hydration process. After casting of concrete, it is possible that water added during concrete mixing may evaporate, specially when the surface area of cast concrete is large and the humidity in atmosphere is low. We add additional water by ponding, spraying or else so that water loss is compensated and hydration can continue. Sometimes it becomes difficult for us to ensure continuous moist curing of cast concrete. What is the implication of discontinuous curing on strength attainment feature of concrete? We have seen that concretes made of coarse aggregates with higher porosity are less sensitive to discontinuous curing. The water contained within the pore space of coarse aggregate cures the cement paste at the aggregate boundary. Thus, for attaining the strength, brick aggregate concrete suffers a bit less than the stone aggregate concrete at the event of intermittent curing.
Recycling of Demolished Concrete
Natural resources in Bangladesh are limited but anticipated pace of infrastructure development is quite fast. The changed development scenario of the country further indicates towards maximizing the land use through demolishing old low-rise structures with the high-rise ones. Recycling of demolished concrete can save the environment further by efficient and cost effective management of generated solid wastes.
We conduct Research and Development activities with the following objectives:
- Obtain a reliable and cost effective method of producing aggregates from recycled concrete by using locally available indigenous technique.
- Determine the fundamental material properties of recycled aggregates produced from stone aggregate concrete, brick aggregate concrete.
- Development of mix design methodology for recycled aggregates.
- Study the effect of discontinuous curing in concretes made of recycled aggregates.
- Development of NDT correlations e.g. Rebound Number vs. Concrete Strength, Resistance to Penetration vs. Concrete Strengths for recycled aggregate concretes in Bangladesh context.
Residual Cementing Properties in Recycled Concrete
Bangladesh is a densely populated country depending largely on her agricultural products. In this country, there is an upcoming need to demolish the old low rise buildings and replace those with high rise ones for housing its increasing population and gradual industrialization. Recycling stone and brick aggregate concretes by crushing and converting them into coarse aggregates and fines for use in new concreting is an established trend.
Hydration in concrete continues over time as along as enough water is available to react with different components of cement. However, the rate of hydration slows down significantly with time. The reaction rate is governed by the composition of cement, temperature and the effective surface area of cement particles. In all cases, we know from electron microscopy that the only outermost surfaces of a cement particle is responsible for hydration whereas interior sections remain eventually unhydrated. Under favorable condition, the unhydrated fraction of cement grains can give additional strength. It is known as the residual cementing property. When we are recycling the concrete, it is perhaps possible that some unhydrated fractions of cement grains can take part later in the process of hydration. When cements also contain pozzolans, the phenomena is much more expected. We are working to evaluate the latent cementing properties in recycled concretes in the context of cement chemistry and material science. The outcome is important from energy and resource recovery viewpoint.
The fundamental contribution of Prof. Amin on identifying the occurrence, origin and quantification of residual cementing properties of recycled aggregates and fines from demolished brick and stone aggregate concrete open the door for appropriate utilization of existing resources. This will not only promote saving of cultivable land by reducing the demands of clay bricks used for new concrete making but also extends the possibility of reducing the cement content while using recycled aggregates and fines. All these points do have significant counts in the context of environmental protection and conservation of nature.
NDT Correlations for Compressive Strength Assessment of Concrete
To determine the in-situ compressive strength of concretes, rebound hammers (Schmidt hammer) and Windsor pins (Resistance to Penetration Tests) are commonly used. However, the correlations between the rebound number, penetration value and the compressive strength depend strongly on the test condition and aggregate characteristics. We have developed the correlations in Bangladesh context so that the reliability in strength prediction can be enhanced. The outcome is important in the assessment of existing buildings for extension, renovation, repair or further strengthening.
Dynamic Behavior of Pedestrian Bridges
Footbridges are now becoming an integral part of a modern city infrastructure. These bridges allow safe transfer of pedestrians over the urban roads, city waterways or highways by providing a segregated grade separated transportation facility in walking mode. Furthermore, in some applications, the bridges of this class also connect urban installations at different elevations.
In the current trend, the architects, in the design process carefully consider the aesthetic appeal of these bridges to maintain a harmony with the surrounding infrastructure. The structural engineers follow the current design codes to ensure the stability, safety and durability of such facilities.
The construction of 332m long three-span Millennium bridge having a notable architectural appearance built over the Thames at London is a recent example. However, on the eventful opening day of the bridge with a large crowd trying to use it, the Millennium Bridge oscillated significantly due to vibration. It was induced due to pedestrian movement. On the eve of a new millennium, the event made the scientific and engineering community over the world realize the necessity to further sharpen their views about the nature that interacts with our built environment. The dynamic stability of the structures due to human movement induced vibration came into focus. Following that event, several studies have been carried out. These studies led to significant modifications of the code provisions for the footbridges.
Nevertheless, the efforts of the architects and structural engineers in coming up with new and innovative designs have not ceased in the recent days. In 2004, a similar footbridge has been designed and constructed over the Crescent Lake at Dhaka, Bangladesh by considering the recently improved code provisions. We compared and reappraised the code provisions as of today for foot bridges, the newly proposed dynamic loads in different codes and the responses for different bridge forms obtained from dynamic analysis.
Failure Analysis and Forensic Investigations
Major reasons behind the poor performance of a structural element that may lead to a partial or even a complete collapse!
- Under design
- Incorrect construction
- Ageing, decay and environmental degradation
- Poor maintenance
- Accidental loads or third party action
Results of a forensic investigation help civil engineers to discover the reasons responsible to trigger unfortunate event and also to uncover the complete story of failure. In this way, we can reanalyze the structure to regenerate the collapse scene and mechanisms. NDT techniques can help us to assess the as-built rebar layout, concrete and steel strengths. Finally, we can piece together all gathered information and analysis results to imagine the fateful scene, identify the responsibilities. We can take lessons for prevention of incidents in future.
Polashbari Incidence: Identification of Collapse Mechanism
One 9-storeyed sweater factory building owned by Spectrum Sweaters Ltd., located at Palashbari Village under Savar Thana of Gazipur District, Bangladesh collapsed at around 1.15 am on April 12, 2005 killing more than 60 and wounding more than 100 persons. The nation was deeply shocked of the incident. The Government also took the matter with proper attention. The Hon’ble President and Prime Minister of the Government of the Peoples’ Republic of Bangladesh visited the site a short time after the incident. Soon after the collapse, the Fire Brigade, Army Engineers Corps of Bangladesh Army and different agencies started the rescue operation. The operation continued till 19th April 2005 (for 8 days) when all the debris over the fallen building was cleared and all the trapped victims were rescued and the dead bodies were recovered.
Checking the design adequacy
With a view to find out the real causes of failure, an independent design of the structure by taking into consideration the as-built column layout, adopted flat plate-column structural form, recommended material specification mentioned in the original designer’s design sketches, end use of the constructed facility and site location. To do this, a finite element model of the structure was developed. The Bangladesh National Building Code (BNBC 1993) was consulted to assign the dead load, vertical live load, wind load and earthquake loads in the process of analysis.
The design trial suggested that the structure was inadequately designed for the following aspects:
- The column sections were under designed at all story levels. The reduction of column section at upper story levels made this situation much more difficult.
- The structural system had no effective lateral load resisting system to limit the sway of the structure within acceptable limits under wind or earthquake loads. Not to mention, the so-called shear wall of the structure built at the extreme west side of the building was not structurally connected with the slabs or columns. Neither any design detail or any proposal for this shear wall was available in the designer’s design sketches.
- In general, most of the slab-column connections at upper story levels were found to be inadequate against both punching and lateral shears.
Different phases of the collapse sequence were simulated due to the removal of the north-east corner column support. The figure shows that due to this support removal, hinges start to form at the slab-column connections in a gradual fashion starting from the top story. However, formation of such hinges were found to be mostly concentrated in the top most four stories (Story 5, 6, 7, 8), except the north-east bays where hinges were found to be developed in all story levels. This largely matched very closely with the Available Information Bases for Investigation indicating the closeness of the simulation results with the real phenomena that took place at that sad hours. Based on this findings, the investigation team was able to derive the following conclusions:
- Either the failure of the northeast corner column or its foundation system (or both) is (are) responsible for triggering the collapse of the structure at that fateful night.
- Upon the triggering, the hinges started to form at slab-column connections at top story levels pushing the upper floors to fall in a sway motion towards east to north-east direction. A mild sway of the southern side columns to southward direction also took place.
- The collapse of the upper floors caused a tremendous vertical impact on the lower stories. This action caused the lower stories to come down vertically.
- North-east corner bays of the structure collapsed vertically at all floor levels.
- The north-east side corner column location need to be excavated to find out what really went wrong on 12 April 2005 at 1:15 am.
- The subsequent revelations through field excavation were completely in line with the simulation predictions. The fact that connection between the column and pile cap failed primarily due to very weak concrete strength associated with defective construction practice.
Failure of Shore Piles in Sadharan Bima Bhaban, Dhaka, Bangladesh
A three basement multistoried building was under construction at Motijheel Commercial Area, Dhaka, just adjacent to Bangabhaban (President’s House, Bangladesh). The bulding is to house the head office of sadharan Bima Corporation, the state owned general insurance company of Bangladesh. Due to heavy raining, the shore piles of the building under construction (2005) failed. Subsequent analysis showed inadequacy of bracings installed to brace the shore piles.
Devices for Measurement and Specimen Preparation
Determination of Chemical Composition of Heterogeneous Matters using Energy Dispersive X-ray spectrometry
In obtaining reasonable measurements, it is important to prepare the specimens perfectly. Sometimes, it becomes a part of scientific art rather than a pure science. We mastered techniques to obtain the chemical composition of heterogeneous compounds via energy dispersive X-ray spectrometry and electron microscopy. We compare the analysis results with conventional volumetric analysis and atomic absorption spectroscopy to assess the reliability of our techniques.
Measurement of Lateral Deformation in Large Deformation Uniaxial Tests
Measurement of lateral deformation in large deformation uniaxial tests is a difficult task. Specially, in testing the mechanical behavior of rubbers, the incompressibility assumption is used to predict the deformed cross section under loading and thereby to calculate the true stress. There are, however, cases where rubbers can undergo considerable volumetric deformation in large strain experiments. Microstructural investigation through a scanning electron microscope conducted on a void-filled natural rubber specimen clarify the effect of voids on the compressibility feature. The microstructure of the natural rubber is observed qualitatively and quantitatively in uniaxial tension and compared to the microstructure in the undeformed condition. We confirmed the existence of the compressibility feature in the void-filled rubber from a microstructural viewpoint.
The findings indicated the necessity of accurate measurement of the deformed cross section in mechanical tests to obtain the true stress. To this end, an experimental setup capable of measuring the deformed cross section of the rubber specimens subjected to large uniaxial compression was developed. To do this, the accuracy of laser beams is utilized for measurement of distance and a mechanical jig is developed to synchronize the movement of laser transducer with the vertical crosshead of the load cell of a computer-controlled servo-hydraulic testing machine. Thus the constraints associated with the conventional strain gages in measuring large strains were overcome.
Testing of Spun Reinforced Concrete Pipes
We have developed the hydraulic jack controlled Test Set-up to assure the quality of Vitrified Clay Pipes and Spun Reinforced Concrete Pipes as per International Standards that approves Three point Loading test systems. In the set-up full scale pipes up to 1.8m in diameter and 1.8m in length can be tested.
Islam, M. M., Choudhury, M. S. I., & Amin, A.F.M.S. (2015) | Amin, A.F.M.S., Hasnat, A., Khan, A.H. & Ashiquzzaman, M. (2015) | Islam, M. M., Choudhury, M. S. I., Abdulla, M., & Amin, A. F. M. S., (2011) | Amin, A.F.M.S., Haque, M.M., Siddiqi, M.Z.R., Rahman, M.A., Islam, M.S., & Alam, M. K., (2012) | Amin, A.F.M.S., Alam, M.S., Okui, Y. (2003)