For people, cities have been priority destinations to explore their opportunities in education and business. This influx of people coming into cities led to the constraint of space. To address this constraint a solution that was explored and is still being practiced is vertical expansion i.e. construction of high-rises and tall buildings. These vertical expansion accommodates offices as well as residences, hotels, and shopping malls. But this leads to increase in population density, which in an event of a disaster is a public safety issue as well as a concern for economic continuity. The impact of disasters to the public cannot be underestimated, for which design professionals need special considerations in their designs and incorporate state-of-the-art technologies and tools.

Considering the impact of disasters especially earthquakes to tall buildings, experts at the Asian Institute of Technology (AIT) carried out research as well as collaborated with partners to provide technical support in the area of Performance-based Seismic Design of Tall Buildings. This support is currently being offered through AIT Solutions, which is an outreach center established by AIT to connect with industry and community partners to spread AIT’s expertise in engineering, technology, infrastructure, and knowledge transfer activities.

AIT Solutions has worked with partners and collaborators in over 130 tall buildings in the Asian region, wherein its team has carried out PBD for different types of structural systems, some of which do not strictly conform to all prescriptive provisions of building codes and verify that the structure meets the stated performance objectives and provide a level of public safety and overall building ductility requirements equivalent to that of a building that follows the prescriptive building code requirements.

With the experience in working on several tall building projects, one aspect that stands out in successfully achieving PBD implementation is the timing and collaboration between the design professionals. The timing and collaboration between the design professionals (architect, structural design consultant, PBD consultant, PBD reviewer, site-specific probabilistic seismic hazard assessment consultant, wind tunnel consultant, and geotechnical engineer) is important to complete the design on time as well as minimize multiple design iterations. PBD peer reviewer should be engaged at an early stage of the project, PBD peer reviewer should review the work of structural design and PBD consultants phase by phase from the early stage of the design process. Upon substantial completion of the structural design by the structural design consultant, PBD consultant evaluates the performance of the building using the seismic input provided by the PSHA consultant. PBD consultant then provides the evaluation results and recommendations to the structural design consultant to modify and update the design.

In initial assessment of analysis results, global responses of the building, i.e. base shear, transient drifts, residual drifts, lateral displacements, are checked for different levels of earthquakes. Transient drift is the maximum drift that occurs within the entire duration of oscillation of the building while the residual drift is the permanent story drift when the excitation stops. Residual drift is checked to prevent excessive post-earthquake deformations which will pose potential hazards to surrounding buildings and lead the censure from building authorities. Lateral displacements are checked to prevent the pounding with adjacent buildings. Each structural component in lateral force resisting system, i.e. foundation, columns, shear walls, coupling beams, diaphragms, beams and columns in moment resisting frames, is evaluated in terms of strength capacity and ductility requirements to prevent the deleterious effects on components to carry gravity loads. Since the performance of the building is explicitly evaluated in PBD to resist the strongest earthquake ever likely to occur, marginal analysis is carried out in design optimization without large safety margins, for the use of construction materials, and for cost effectiveness and sustainability of limited natural resources while meeting the performance objectives of the design.

To know more about how we support our partners and collaborators during the Performance-based Seismic Design evaluation of buildings, contact us at: solutions@ait.ac.th.

]]> http://solutions.ait.ac.th/performance-based-seismic-design-of-100-buildings-what-does-it-tell-us/feed/ 0 http://solutions.ait.ac.th/a-well-kept-secret-in-structural-design-revisited/ http://solutions.ait.ac.th/a-well-kept-secret-in-structural-design-revisited/#comments Fri, 31 Jul 2020 04:43:46 +0000 http://solutions.ait.ac.th/?p=13632 By Dr. Naveed Anwar

I wrote this article on moment-curvature curve as being a well kept secret in structural engineering, a few years ago and gauging from the interest it had raised, I thought of updating it and complementing it with a video to demonstrate some of the ideas discussed there.

You can find the original article here.

One of the interesting developments since the publications of the previous article is the generation of the “curvature capacity surface” (shown in the background image above), which shows the variation of the maximum curvature capacity of a cross-section along various bending directions and its relationship with axial load. This surface is not widely available or discussed, but can provide a good understanding of the ductility of the cross sections sections, subjected to axial load and bi-axial bending, such as columns and shear walls. It also shows how rapidly a beam behavior changes to column behavior as the axial load crosses about 10% of the capacity

Another valuable insight that the moment curvature curve can help to provide is the understanding of various types of stiffness (initial, tangent and secant) and its variation with moment and curvature, which can reduce rapidly (even becoming negative!) after reaching the yielding capacity. This effective stiffness can then be used for computing rotations and deflections, and for nonlinear modeling and analysis.

In addition to looking at the relationship of curvature to moment, the same procedure and process can also be used to plot the variation of maximum and minimum strain, axial force in compression and tension, corresponding stresses and neutral axis depth with change in curvature. Such plots can provide significant insights into the cross-section response and help improve the design and evaluation of reinforced concrete members.

With increased focus on displacement based and performance based design and evaluation of structures, the role of moment curvature curve and its applications are becoming even more important. So, let us keep exploring this versatile tool, and keep finding more treasures hidden beneath it!

Related post: https://www.linkedin.com/pulse/well-kept-secret-structural-design-naveed-anwar

By Chanthoeun Chiv

My mentor/senior always keeps reminding me about utilizing one’s engineering sense to judge the results from the analysis. After pushing the “run” button, the first thing you should do is not about rushing to play with “design” option to obtain the amount of the reinforcement, but to look at the deformed shape of your structure, does it deform the way it should be? Are there any nodes floating alone like a roller coaster? Do the time periods of the building make any sense to you? How about checking the reaction due to dead load only to see whether the selfweights are actually transferred to the foundation? SFD and BMD for specific case? These are the fundamental questions you should be asking yourself prior to jumping to use the analysis results directly from the commercial softwares without careful discretion, otherwise you will be just a software operator or a robot who just knows how to throw garbage in and wait for the garbage out. If you keep doing so, you will be putting your career on the line and can’t inevitably avoid facing the worst disasters afterwards if something really bad happens.

Structural engineers are explicitly responsible for the buildings he/she has designed, one needs to be able to read the analysis results and interpret them professionally. But why most of the time, we are usually perceived by the supervisors/mentors that we are lack of engineering sense/judgement? Is it fully our fault? Is there probably any hidden reason behind it?

I believe it’s of paramount significance to inject novel content and creative methodology into the conventional and out-of-dated learning methods student used to be taught at school particularly for structural engineering curriculum. Why I say so?

Base on Dr.Graham H.Powell, Professor Emeritus of Structural Engineering from UC Berkeley, there are three distinct phases in structural analysis such as:

1) Modeling

2) Computation

3) Interpretation

Prof.Graham H.Powell believes (and you may want to argue later) that the most important phases are No.1 and No.3, and the least important one is No.2. However, what we have been taught extensively at school was how to do “computation”, but giving little attention to “modeling” and “interpretation”. The skills being needed and useful the most are not taught while the skill with the least importance level has been inherited down in the exact same old way like it used to be decades ago. So I think something should be done, a reform must be implemented to promote these two needed skills. By doing so, the young engineer could be exposed to the most important skills early and they could enhance and/or improve their skills accordingly in order to fulfill the gaps left out from school.

1) Modeling
The structural analysis is carried out on the “model” of the actual structure, not on the actual structure itself. There are a number of key points need to be addressed as follows:

1. What you draw in the software is just an “approximated” model of the real structure, it does not necessarily represent the “exact” behavior of the actual one, but it should capture the crucial “aspects” of the real structure’s behavior.
2.  Always employ “node-element” model
3.  Choosing appropriate element, assigning with corresponding properties like stiffness and strength
4.  Choosing the appropriate demand/capacity measure for performance evaluation.
5.  3D model may looks splendidly appealing with colorful rendering. However, it doesn’t mean it has the exact same behavior as the real structure, keep that in mind!

3) Interpretation
After finishing modeling of your structure, computation of the model will be taken care by the computer. At the end of the computation phase, a set of “results” will be provided and that is the time the structural engineers start using their hard-earned skills from school to “interpret” these “results”. There are a number of key points need to be addressed as follows:

1. There is no one-size-fits-all procedure for interpreting the analysis result.
2. Use demand/capacity ratios (DCR) to help make design decisions.
3. Always being skeptical about your analysis results.
4. The results from your analysis model isn’t for the actual structure, it doesn’t have to be, and it will never be. However, as a structural engineer, our job is to look for the results that are close enough for practical purposes.

2) Computation
Anything that is neither included in “Modeling” nor “Interpretation” is to be coined as “Computation”. A number of key points are to be addressed as follows:

1. For current scenario, almost every structural engineers are using computers to do the “computation” part.
2. Basic understanding of the computation phase like equilibrium equations, compatibility and the boundary condition is necessarily needed. Even the structural engineers rely heavily on the skill and expertise of computer program developers, they can’t go away from these fundamental knowledge in structural engineering.
3. Only those who write the computer programs require an in-depth knowledge about the computation phase. We, the users of the program, do not need that skill.

Long story short, it’s easy to be seduced into believing that what we draw in the model is an exact representation of the real structure. Therefore, we need to be skeptical about the outputs obtained from the software. We need to know what we throw into the computer with acceptable understanding of the assumption inside the software, and remember this old saying: “garbage in, garbage out”. Indeed, for the time being, “modeling” and “interpretation” are archived from hands-on experience as well as merely from the job training. However, what if students/young engineers could get exposed to these two needed skills since they are at school, it would be extremely helpful for their work in the future. The least/minimal supervision for the freshers will be able to be implemented effectively and economically.

Related post: https://www.linkedin.com/pulse/garbage-out-chanthoeun-chiv/

#GIGO #StructuralEngineering #YoungEngineers #Freshers

Hokkaido Japan Earthquake

Date: September

Area: Northern Japanese Island of Hokkaido

Death Toll: 40+

Cause and Damage: The magnitude 6.7 earthquake struck before daybreak of 6 September and knocked out power and train service across Hokkaido, home to 5.4 million people. Nearly 3 million households lost power, according to the Hokkaido Electric Power Company. It took two days to restore electricity to most households.

Source: https://www.washingtonpost.com/world/asia_pacific/

Lombok Indonesia Earthquakes

Dated: July and August

Area: Lombok, Indonesia

Death Toll: 500+

Cause and Damage: A destructive and shallow earthquake of 6.9 magnitude struck the island of Lombok, Indonesia. It was the main shock following its foreshock, a nearby Mw 6.4 earthquake on 29 July and was followed by another 6.9 earthquake on 19 August 2018. The epicenter was located inland, near Loloan Village in North Lombok Regency. Its rupture spread to the north and reached the sea, creating tsunamis. Severe shaking was reported throughout the entire island, while strong shaking was reported on the neighboring islands of Bali and Sumbawa.

Source: https://reliefweb.int/disaster/eq-2018-000122-idn

Fiji Earthquake

Dated: August

Area: Ndoi Island, Fiji

Death Toll: Not reported

Cause and Damage: A 7.9 magnitude earthquake has struck the holiday island of Fiji in August. The quake was centered about 281km north of Ndoi Island with a depth of 559.6km.

Source: https://www.news.com.au/travel/travel-updates/incidents/massive-earthquake-rocks-fiji/news-story/0b35939ce91a9117cb41bb772c6a4c90

Oaxaca Mexico Earthquake

Dated: February

Area: Oaxaca, Mexico

Death Toll: 14+

Cause and Damage: The 2018 Oaxaca earthquake of 7.2 magnitude occurred in the Sierra Madre del Sur in Oaxaca state in Southern Mexico. The hypocenter was located at a depth of 24.6 km and approximately 37 km northeast of Pinotepa de Don Luis. Oaxaca lies on the destructive plate boundary where the Cocos Plate is being subducted beneath the North American Plate. In the region of this earthquake, the Cocos Plate moves approximately northeastward at a rate of 60 mm/yr. The earthquake occurred as a result of thrust faulting at a shallow depth. The helicopter was also crashed during the earthquake.

Source: https://en.wikipedia.org/wiki/2018_Oaxaca_earthquake

Papua New Guinea earthquake

Dated: February

Area: Hela Province, Papua New Guinea

Death Toll: 160+

Cause and Damage: A 7.5 magnitude earthquake occurred in Hela Province, Papua New Guinea and the epicenter was 10 kilometres (6.2 mi) west of the town of Komo. Papua New Guinea lies within the complex zone of collision between the Australian Plate and the Pacific Plate, which converge at a rate of 107 mm per year at the earthquake’s location. An assessment have shown significant damage and large landslides, and it is estimated that up to 465,000 people may have been affected by the disaster. A major aftershock with a magnitude of 6.2 M occurred in the Southern Highlands province close to the location of the earthquake.

Source: https://reliefweb.int/disaster/eq-2018-000020-png

Earthquakes cannot be prevented and sometimes are predicted incorrectly. But the effects of earthquakes particularly for infrastructure can be reduced by having innovative structural systems. These systems, however, require practicing engineers to have great expertise, skills, and computational capabilities. To address the issues related to safety of cities and infrastructure, the 7th Asia Conference on Earthquake Engineering (7ACEE2018) is being jointly organized by the Asian Institute of Technology (AIT) and Engineering Institute of Thailand (EIT) in collaboration with the Association of Structural Engineers of the Philippines, Inc. (ASEP) and supported by Computers and Structures, Inc.(CSI), European Union, and Mahidol University. The Conference will be held at Sheraton Grande Sukhumvit, Bangkok, Thailand from 22-25 November 2018.

Registration for this conference is still open. Be sure to register at http://acee2018.org/ or contact aceesecretariat@ait.asia for more info.

Photo credit:  Associated Press Photos

My participation in the 2018 ICT Innovative International Summer School held in Xidian University, Xi’An, China has given me a lot of memories, friends from various countries across globe, and a complete different experience I would not forget. The summer school provided a unique opportunity to interact with influential people in my area of specialization. It was a wonderful opportunity to represent my institution such that people from various people can understand about the activity that an institution is involved. I was more than honoured to have a chance to represent my institution as a student of AIT as well as a student intern at Innovation Lab, AIT Solutions that provided my air ticket to China.

The summer school consisted of 61 students from outside of china and 65 Chinese students. The international students joined from more than 15 countries majority of the participants from Europe. The organizing committee was very helpful in providing all our needs of its international participants. Each international student was assigned a Chinese partner for safety and comfort. My Chinese partner was very much helpful in delivering all the help needed right from getting a Chinese sim-card, translating Chinese for local vendors and much more. They even picked me from airport to hotel.
The camp was held for ten days. Every day was filled with joy and learning. During ten day we learnt about the entrepreneurial spirit in china the opportunities for a business in china. There were various initiatives to encourage entrepreneurs. The lectures were filled with inspiring journeys of various renowned professors and management of Huawei Company. The lectures from various professor inspired taking research into end products. Research to solve problems.

The schedule was planned in such a way that a lecture is followed with field trip or and activity which may be group activity or an individual with Chinese partner guiding the international students. The activities helped to interact with our participants and discussing about the research at their university and vice-versa. The Chinese partners were sharing lot of their experience and knowledge about china. They were discussing about lot of political, geopolitical issues, culture traditions.

There are various field trips to museums, co-working spaces in Xi’an and various company visits. The Museums and their history can give a completely difference outlook of china as compared to their technology outlook. The co-working spaces in china are driving their youth to develop good product which can serve the gap in the society. The visit to companies on a whole is good experience.

The other activities included Radio Direction finding sport and Radio making from scratch. These activities have been very unique of its kind. In terms of learning these activities have a good learning curve within. Building was a great activity to plan. Development of circuitry was a great idea. The university has an in house circuit printer which enables them to work various research areas.

On the very last day we had graduation ceremony where every person would be presenting about their organization, country and their experience during stay in China.

This was a very great opportunity for me to present about AIT and Innovation. As our Institution has a co-working space for students to nourish their creativity and provide working environment where they can test their ideas. The area which [iLab], AIT Solutions is concentrating is not addressed by many organizations across the worlds but the area has a tremendous ability to transform major world problems. Along with presentation there was students were to collaborate in solving the problems of waste management and recycling the waste through the path of technology. Specific topics I highlighted during the presentation were:

• Bottle shredder and can crusher
• Haptic walking stick
• Tele-rehabilitation arms
•  IT projects
• Civil and Structural engineering projects

The presentation drew attention from many people who said that the attempt to solve the problem of waste management was inspiring. Many of the Chinese students were interested about the projects at AIT Solutions.

Tarun Pulluri
[iLab], AIT Solutions
Asian Institute of Technology

 As a structural engineer, it had me thinking, would it not be great to be able to do such a quick check with our structures as well? How can we treat our structures as doctors treat their patients? Can we check their pulse rates? Can we listen to their heartbeats?

And it occurred to me, that we can and probably, many of us already do. Well not literally, but in a manner of speaking, if we think of the natural frequency of structure as its heartbeat. Just like the number of heartbeat per minute is a reliable, and extensively used indicator of human physical fitness, the natural frequency (number of cycles of vibration per second) of a structure is a fairly reliable indicator of its structure’s stiffness, damage state and overall health. For example, like the normal heartrate of a healthy person at rest should be between 60 to 80, a free vibration frequency of a tall buildings of say 30 stories should be about 0.25-0.35 hz or a period of vibration of 2-3 seconds. If the heart rate is too fast for a human being, it may indicate stress or abnormal conditions, and if too low, may indicate health issues. In the same the way, if the frequency of a structure is too high, it may indicate an abnormally stiff structure, and a low frequency may indicate soft or weak state.

Just to be clear, this free vibration response is often obtained using what is called the “Modal Analysis” of a structure. Before we discuss some of the applications where the vibration characteristics (or the results obtained from the modal analysis) can be extremely useful in structural engineering, let’s first take a quick look how at how it all started. The basic idea and the origin of modal analysis can be traced back to the times of Sir Isaac Newton (1643 – 1727) and Joseph Fourier (1768 – 1830). The essential concept is that the dynamic response of physical objects can be described as a sum of few simple waves. Lord Rayleigh (1842 – 1919) developed the concept further and presented in his book “The Theory of Sound”, published in 1877. Later, an Italian structural engineer, Arturo Danusso (1880 – 1968) made key contributions in earlier 20th century to introduce and apply the basic concepts of modal analysis, originally developed in acoustic theory,  to describe the dynamic response of building structures against earthquakes.

The free vibration analysis of a structure involves the determination of its natural frequencies, mode shapes, and modal participation factors. Vibration mode shapes are the “shapes” in which the structure would like to oscillate (with corresponding natural frequencies), if allowed to vibrate freely. Each mode shape is an inherent property of the structure and is completely defined by its mass and stiffness. If a linear elastic structure is deformed into a linear combination of few mode shapes and released to oscillate freely, every mode will be independently present (with its own natural period) in the resulting combined time history of deformation. This is the key concept behind the notion that the combined vibrational response of any structure can be decomposed into contributions from few vibration modes, each behaving (and can be solved) independently. The degree of participation of a certain mode in the overall vibration is determined by the characteristics of excitation source(s), and spatial distributions of the mass and stiffness of the system.  But I am sure, you already knew that!

You might  also know, that the modal analysis has profound applications in diverse areas, covering civil engineering, mechanical and aeronautical engineering, industrial and manufacturing engineering, biomedical engineering, acoustics, space structures, electrical engineering, and so on. The traditional engineering designs require the structures to be lighter in weight, and yet strong-enough to sustain external excitations. These requirements can easily make them susceptible to undesirable vibrations. In such cases, a proper consideration of dynamic response becomes a key factor in design. Nowadays, the use of versatile finite element solvers have opened a whole new paradigm where the modal analysis is finding its innovative applications – from car manufacturing on one side, to the non-destructive testing of high-rise buildings on the other side – from the design of space structures to scientifically evaluating the violins and guitars, and even studding the human heart and the movement of the brain mass within the skull.

Having said that, I would now like to talk a bit more about the significance of modal analysis as applied to the structures, emphasizing the importance of underlying “heartbeat” for the structures. This can help us to:

• First, and foremost, gain an insight into the complex dynamic response of a structure. The experimentally determined natural periods, damping factors and mode shapes can provide an important information regarding the structural characteristics, which can then be used to convert the detailed structural models in to simple modal models.
• And equally important, it helps to provide a quick check on the analytical structural models. For example, if the natural period computed for the model is not what is expected, then the model data can be checked. Most common errors such as incorrect mass density, or wrong elastic modulus (both caused sometimes due to unit confusion, and sometimes wrong material type,) can be detected.
• The plot and animation of mode shapes of modal analysis, in addition to being fun to watch, can help to detect the disconnected members, structural irregularities, eccentric response, torsional modes etc.

(See Ashraf Habibullah, the President of Computers and Structures Inc, CSi, discussing the role of animations in structural engineering on this link. https://www.youtube.com/watch?v=SGa1wzZEUsQ)

• The detailed finite element models of structures can be calibrated with the modal data (natural periods, mode shapes etc.) which is either obtained experimentally or is statistically derived based on some large-scale experimental studies. The modal model is expected to represent the close-to-real dynamic behavior of a structure and therefore, can be used to “correct” the finite element model.
• At the design stage of new building structures, the optimum dynamic response can be easily obtained by altering the mass and stiffness distributions. Various modifications, based on the “what-if” analysis, can be proposed, which can then help in selection of an optimum lateral-load resisting system for a building.

And if that is not enough of reasons to do a modal analysis, either analytically through software, or physically through measurement, we have some more advantages:

• The modal analysis can be used to predict the response of linear elastic structures against a given dynamic loading. Similarly, it can also be used in reverse to predict the dynamic forces against a given measured vibrational response of the structure. With a known dynamic response, the fatigue life of a structure can also be predicted with a reasonable accuracy.
• The modal parameters can be used to detect the damage (cracking or yielding etc.) in structure, thus leading to structural health monitoring (SHM). Any reduction in stiffness because can be easily detected, measured and analyzed by the change in modal properties. The systematic comparison of modal properties before and after structural damage can be used to develop useful relationships for this purpose. An important example of such applications is the regular bridge monitoring and maintenance using ambient vibrations.
• And, perhaps, the most important application of modal analysis in structural engineering is in the design of control mechanisms to suppress unwanted dynamic response of structures. The analysis and application of almost all control devices (dampers, actuators, sensors etc.) require a detailed knowledge of free vibration response and modal characteristics. The engineers can play with natural frequencies, shift them to desired values, change the mode shapes, and relative contributions of different modes, to obtain the optimum structural response.

An interesting video showing various mode shapes of a 40-story RC shear-wall buildings can be seen here https://youtu.be/DnBnckVMztg. This example shows how visualizing the free vibration response can be not only fun to watch (music added!), but also helpful in developing the feel of dynamic behavior and the relative contributions of different vibration modes to the total dynamic response.

We can all appreciate that the ever-growing real-life complexities, and structural demands in buildings and infrastructure are posing new challenges to civil and structural designers. These require developing a feel for the structural response, a greater understanding and expertise in analytical and design procedures and development of out-of-the-box solutions

So, let’s start listening to the “heartbeat” of our structures, and understand what they are saying!

An event that will be introducing modern vertical design in high rise buildings while maintaining the heritage feel and local community values, Marcus Evans 6th Annual Vertical Cities is definitely a must attend event in Dubai this March. Don’t miss the Dr Naveed Anwar presenting on ensuring safety and higher performance of tall buildings for rare and strong earthquakes.

In conjunction to the event, Dr Naveed who is a CEO/Executive Director Solutions at Asian Institute of Technology at Thailand shared his thoughts on challenges faced in the ASEAN region as well as mitigate risks in the current environment.

In your opinion what are the challenges faced while introducing cutting edge vertical design in your region?

The continuous population growth, and accelerated urbanization in almost all major large cities and townships in Asia is dictating the need for vertical design and construction solution for housing, work spaces and multiple usage. In the ASEAN region, where most our work is focused, tall buildings are sprouting at an ever-faster rate. However, in many cities, lack of local design expertise, construction technologies as well as the traditional mind set are proving to be challenges to overcome for very tall and vertical solutions. In some cities, the lack of mass transit system provides transportation and commuting difficulties to vertical design clusters. The affordability and need for such hi-tech and cutting edge development is another challenge, with uncertainties in economic development, and memory of collapse of previous real estate bubbles.

How do you develop a systematic approach to avoid implementation bottlenecks?

Many of the challenges are related to the overall urban policy and planning issues, and often difficult to solve only through architectural or engineering solutions. As we work mostly on the safety and improving disaster resilience through application advanced and extended approaches such as performance based design, wind tunnel testing, this is systematically included in the design practice through engagement with the architects, structural engineers, and most importantly with the developer and even the ultimate occupants to raise the awareness of higher safety and performance expectation for tall buildings, as they house many people as well as high value assets. This awareness, and exposure to advanced design approaches and technologies helps to smoothen the adoption and application and raises the overall state of the practice and improves the performance of the vertical built environment

From your past experiences, how do you mitigate risks and deliver results that matches future trends?

Most important is to be aware of the future trends, by keeping a close tab on the developments in various parts of the world, and their present or future relevance to our region and state of local development. Often, adoption of solutions elsewhere in local context, without careful adaptation and localization presents a risk in its long-term success. Being part of an industrial interface arm of an academic institution, provides a great opportunity to do relevant research derived from partial application, and develop solutions, which are well adapted and customized for future application. We generally start a parallel research project for every important design challenge for in-depth understanding and development of solution with local relevance. This significantly reduces the risk with use of new technologies and adoption of upcoming trends and meeting future demands. My current topic in the event on integration of performance based design for strong wind and earthquakes is such an effort.

Any added views that you wish to highlight on your upcoming presentation at this event?

Currently, there is a significant interest and use of performance based design for strong and rare earthquakes. However, the design for wind is still based on traditional or conventional approaches, creating a disparity amongst the design procedures and inconsistent evaluation of expected performance and safety for the occupants, as well for the protection of valuable assets in the tall buildings. This will become more relevant in future, as buildings get taller, and are constructed in high-hazard prone area, as well to mitigate effects of climate change. My current topic in the event on integration of performance based design for strong wind and earthquakes an area of current interest to many engineers, but is not yet part of standard design practices.

How do you find the right balance while designing buildings that are aesthetically pleasing and functional?

This has always been a challenge facing the designers. Creating a balance between the aesthetes and functionality is primarily the role of the architect, and not really my specialization. However, creating balance between aesthetics and structural form and performance is something I can comment. For low rise, or conventional buildings, the architect may preprimary define the aesthetic form, whereas the structural designer may provide the appropriate structural system for safety and serviceability. However, for tall and very tall buildings, a collaborative development of esthetic form and structural form and system is essential. The building aesthetic form effects the wind forces, as well the seismic performance to a large degree. The ideal solution is to integrate structural system and make it part of the aesthetic form. This has been done successfully in many well-known buildings. An attempt to hide structure, in favor of the aesthetic form may impact the performance, as well as cost effectiveness. We often work closely with the architects, understand their aesthetic intention and concept, and offer various solution that fit into or reinforce the concept.

How do you think this conference will contribute as a knowledge platform for this industry?

Planning, conceiving, designing, developing, construction, managing, maintaining and marketing the vertical development and tall buildings requires collaboration and contribution from many experts and stakeholders. Often traditional conferences focus on one or two of these experts and stakeholders, whereas the current event is providing a platform for a wide range of experts, stakeholders including developers and clients. This event will be very useful for developing a common understanding of the issues, as well as to expose each other to the available solutions. It will also help to create network and possibly, teams or collaborations for the future projects. I am looking format to hearing from other speakers, as well interact with the participants.

Click here to read Dr. Naveed’s interview published in Bangkok Post recently.

About 6th Annual Vertical Cities in Conrad Dubai

Happening for the sixth time this year, this Marcus Evans large scale event aims to brings insights on resolving rapid urbanization in highly density cities as a solution for sustainable living. Don’t miss the opportunity of learning how to establish skyscraper buildings as a destination of choice with contemporary designs and unique commercial elements.

Do you know what a moment-curvature curve is? Dr. Naveed Anwar, Structural Engineering Expert asked this question to his post-graduate students in the Advanced Concrete Structures class. Out of forty students, one student raised his hand. He posed the same question to a group of practicing structural engineers, participating in one of the seminars where he was a speaker. He was surprised to find out that very few of them had good knowledge about it.

What is a moment-curvature curve? Dr. Naveed explained this topic in his LinkedIn post titled “Well-kept Secret in Structural Design”

Another interesting post to read related to this topic is the “Is the understanding of Member’s Cross-sectional Behavior, key to understand the Overall Structural Response?”

Engineers who are interested in this subject can also check the book “Structural Cross Sections: Analysis and Design” by Dr. Naveed and Engr. Fawad Najam which focuses on some of the key issues related to the understanding of cross-section behavior, with an emphasis on computer applications.

For those who want to get a copy of Structural Cross Sections: Analysis and Design, you may purchase the book from the following links:
AIT Solutions  | Elsevier |  Google Books |  Amazon

The cross-sections of structural members and their properties are a basic component in almost all aspects of analysis and design of structures. In fact, the primary objective of an efficient design process is to proportion the cross-sections of all structural elements to safely resist the applied load effects and actions. The cross-sectional properties are required a priori to even start the modeling and analysis process for a structure, to prepare initial cost estimates, and even to refine the basic space planning and utilization schemes. Is it then reasonable to conclude that the understanding of cross-sectional behavior of elements is the key to construct efficient, economic and resilient infrastructure? It seems that this may be the case.

The figure on the article header describes the short story of structural engineering, and shows the key position of cross-sections in the overall hierarchy of events involved in an efficient and smart transformation of “materials” in to “structures”. The properties of constituent materials manifest themselves in to the properties (e.g. stiffness and ductility) of cross-sections. The cross-sectional behavior then has a significant role in defining how the member will perform under an applied action/loading. Being an assemblage of individual members, the overall structural performance is determined by the member behavior.

This means that the response of any complex structure against applied loading can be traced back to its cross-sectional and material properties. Therefore, for an effective design of important structural components such as beams, columns and slabs, all issues related to the behavior of cross-sections and their properties need to be addressed in detail. Apart from structural aspects, the cross-sections of beams and columns also affect the planning and construction aspects of an engineering project. In planning context, they affect the space utilization, visibility, lateral clearance, water flow, wind resistance, aesthetics, etc. Similarly, the cross-section sizing and properties also affect rebar cage fabrication, formwork cost and its reuse, construction techniques, and efficiency. If one particular shape may be suitable from structural considerations, it may be unsuitable from planning or construction considerations.

The vital role of cross-sections in overall structural behavior, analysis and design also demands the development of integrated analysis approaches which should have the ability to handle all complex shapes, material behaviors and configurations. With the recent advancements in computing technologies and the applications of information technology in structural analysis and design, several computer-aided cross-section analysis packages are developed. The development of unified analysis procedures to determine axial-flexural capacities and response of cross-sections, is becoming even more important in this scenario.

The growing complexities in structural forms, architectural shapes and the use of materials with innovative properties, are some of the new challenges associated with the analysis of complex cross-sections (e.g. made of composite materials with significantly varying behaviors). For example, the determination of capacity for such a complex cross-section requires to determine stresses in individual constituent materials and then combine to get stress resultants. For a general cross-section, the flexural capacity also depends on the axial load. Due to this interaction of both actions (axial load and moment), we cannot simply determine the flexural capacity of a cross-section under uniaxial bending, as a constant number. Instead, an axial-load vs. moment interaction diagram (also referred to as capacity curve or yield curve) provides all possible combinations of both actions which would result in achievement of a pre-defined limit state. For a relatively more general case of biaxial bending, the axial-flexural capacity is defined by a 3D capacity/yield surface. This interaction of axial load and moment is an important consideration while setting-up a structural model for nonlinear analysis. For the determination of demand-to-capacity ratios for a cross-section against any loading scenario, its complete capacity curve should be defined prior to the detailed analysis.

Another (and perhaps the most important) relationship, showing the action-deformation behavior of a cross-section under flexural action, is the Moment-Curvature relationship. This relationship is the primary input in a nonlinear structural model as a load-deformation behavior assigned to a moment plastic hinge. This accounts for the nonlinear action assumed to be lumped at the location of plastic hinge. It describes the cumulative behavior of all materials and their properties as a combined cross-sectional response. Like any other action-deformation relationship, the moment-curvature curve is also described by different states, each corresponding to a physical condition of cross-section, starting from linear elastic behavior (uncracked) to near-collapse plastic behavior (fully damaged). The valuable insight obtained from the moment-curvature curve in terms of cross-sectional behavior (e.g. brittle, ductile, elasto-plastic, degrading etc.) can be used to predict the member response.

So it would seem that the cross-sectional properties of structural members are in fact the foundation of almost everything, starting from the determination of stiffness, stresses, and capacity, to the computation of response e.g. deflections, curvature and ductility. It is this key contribution of cross-sections that the retrofitting strategies for damaged structures are mainly comprised of increasing the load-carrying capacity and ductility of cross-sections of its members.

A recently published book “Structural Cross-sections: Analysis and Design” focusses on some of the key issues related to the understanding of cross-section behavior, with an emphasis on computer applications. It provides a consolidated and consistent information, insight and explanation of various aspects of cross-section response, analysis and design, irrespective of, but with due consideration to different materials. We hope that such attempts to integrate the textbook knowledge and theoretical concepts with the computer-aided analysis will contribute to better our understanding of structures, and will make the story for structural engineers more interesting, the story starting from “materials” and ending on “structures”.

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