Understanding 2D Structural Analysis

In my computer laboratory class on "Structural Engineering Computer Methods", the students use Structural Analysis software like GRASP, ETABS and SAP2000. Learning to use the software is not the end itself but learning concepts on structural analysis is the primary objective of the course. To achive this objective, I wrote "Understanding 2D Structural Analysis" - an exploratory-type of instructional and learning material consisting of ten modules about modeling and analysis of framed structures in 2D using GRASP. Each module focuses on a specific issue on structural modeling and analysis which is discussed with the aid of graphical and tabular results obtained from GRASP. The set of learning modules is not a substitute to a textbook on structural analysis. The theory is not presented. No derivations or equations can be found. The student or reader must refer to the textbooks for definitions, equations and techniques. Each chapter begins with background information and a “case study”. The reader explores the issues raised in the case study through the “Things to Do” GRASP activities or by simply observing and analyzing the “Observation” and graphical and tabular results presented in the module. Included in the modules are “Things to Try” GRASP exercises and “Things to Ponder” comments on the analysis and design of structures. Using the set of learning modules, the reader or student with the aid of GRASP discovers important insights on the response and behavior of structures due to variations in the parameters of the model and configurations of the structure, changes in member and material properties, and also changes in the restraint and loading conditions. Through the graphical results, the student can visualize the phenomena and this would accelerate his understanding of concepts through the experience of seeing and interpreting solutions to various structural modeling and analysis problems. You may download this book from my website and use it in your class.

Structural Analysis Tips to Popsicle Stick Bridge Builders (Load Application)

Using a structural analysis software like Graphical Rapid Analysis of Structures Program (GRASP ) developed by the Asian Center for Computations and Software (ACECOMS) can help popsicle stick bridge builders in designing their bridges. The behaviour of bridges depends on how and where the loads will be applied. For example, if two concentrated loads will be applied to test a bridge with a truss design, applying the load as shown in the figure at the bottom or uppr part of the bridge will make a lot of a difference. The GRASP software was used to compare the maximum deflection at the bottom horizontal elements of the two bridges. The structures were analyzed as a "frame" since the joints may be assumed rigid because of the glued connections. The deflection for Bridge 1 where the loads were applied at the bottom is 20% higher than Bridge 2 where the loads are applied at the top. For Bridge 1, the bottom horizontal elements have large bending moments and axial forces and diagonal truss members carry large axial forces - the top horizontal members had minimal stresses. For Bridge 2, on the otherhand, the top horizontal elements may have large bending moments but the axial forces are not so large compared to bridge 1. The bottom horizontal elements now contributed more in resisting the loads by carrying more axial forces as compared to bridge 1. The diagonal truss elements of bridge 2 carry almost the same magnitude of axial forces. So before designing your bridges, know how and where the loads will be applied. It will make a lot of a difference in the bridge performance!

Structural Engineering for Kids 4 - Building Up London Bridge

London Bridge is a nursery rhyme where various concepts in structural engineering may be introduced. Obviously, the concept of structural engineering failures is described in this song - London Bridge is falling down. Structural failure this time is described in relation to different types of construction materials. The behavior and strength of various structural engineering materials and members can be described while playing the song - Build it up with pins and needles…Build it up with wood and clay…Build it up with iron and steel.. Build it up with stone so strong. How the structural members fail depends on the structural properties of the materials – brittle materials like concrete break or crush, ductile materials like iron and steel bend or yield. So London Bridge failed in various ways - Pins and needles bend and break…Wood and clay will wash away…Iron and steel will bend and bow… Stone so strong will last so long. Bridge failures, however, depend on many factors as shown in the video below like the structural design of the piers including the detailing of reinforcement, the bridge deck supports, the soil and foundation...

This nursery ryhme may also be a good opportunity to introduce the concept of strengthening and retrofitting of existing structures. So when London Bridge fell, the ryhme continues - We must build it up again, Up again, Up again. We should not wait for another bridge disaster to occur. We should learn form the previous bridge disasters like those that happened to the Tacoma Narrows Bridge in 1940 or the Hanshin Expressway in 1995. We should act now to strengthen and retrofit existing bridges and structures. The last slide in the video clip shows the bridge pier retrofitted against earthquake effects.

Structural Engineering for Kids 3 - The 3 Little Pigs and the Big Bad Wolf - Lessons on Wind Loads

Remember the story of the Three Little Pigs and the Big Bad Wolf? This is a story where kids will learn the importance of designing structures against external forces such as wind due to typhoons and hurricanes. The big bad wolf wants to eat the pigs. And to do that he must be able to destroy each pig’s house by blowing on the house. The big bad wolf represents external wind forces that a house must resist. So to protect themselves, the pigs have to build their own houses. Pig 1 built a house of hay. Pig 2 built a house of twigs, while Pig 3 built a house of stone. And you all know the story’s ending, the big bad wolf’s strong blowing power destroyed the houses of hay and twigs, but not the house of stone. Structural engineers must design structures against wind loads. Codes like the National Structural Code of the Philippines (NSCP) specifies wind zones with corresponding basic wind speeds in determining the design wind loads. For example, Metro Manila belongs to Zone II with a basic wind speed of 200 kph, while the Northeastern parts of Luzon and Visayas under Zone I have a speed of 250 kph. According to the Outdoor Advertiser's Association after the Typhoon Milenyo in 2006 struck Metro Manila, they designed their billboards for 120 kph (PDI Oct. 1, 2006) and this is less than 200 kph. The toppled billboards due to Typhoon Milenyo showed us what will happen to structures not designed, constructed and maintained properly against wind forces. Photo courtesy of Engr. Willy Lopez (DPWH): Fallen billboard due to Typhoon Milenyo 2007

Popsicle Stick Bridge Testing

Popsicle stick bridge building competitions usually choose the winner based on the strength/weight ratio. Usually loads are applied at the mid span of the bridge by placing incremental weights. The load at failure (P) is then determined and divided by the bridge weight (W) to get the bridge performance.

In the DLSU CES Bridge Building Competition, a Universal Testing Machine (UTM) is used to test the strength and displacement of popsicle stick bridges. Since the load will be applied on the bridge deck, an innovative method was devised so that it can be applied to truss bridges. Two 14 mm steel bars spaced at specified distance are placed on the bridge deck. A hollow steel cage is then placed on the two steel bars. The UTM is then applied on the steel cage which then transfers the load to the two steel bars and then to the bridge deck. A displacement transducer is attached to the UTM to measure the displacement (D) in mm. The load is applied and the value of P (kg) is obtained. The value of P can be predefined or when the load dial of the UTM stops which indicates bridge failure. The bridge rating, S = 1000(P/D)/W is then determined. The S rating represents the bridge stiffness (kg/m) per unit weight (kg). For example, the bridge shown in the video below was tested and it’s P = 30 kg, D = 25 mm and W = 1.50 kg. Hence, it’s rating , S = 1000(30/25)/1.50 = 800 (kg/m)/kg. By using the S rating, strength, displacement and weight become parameters in ranking the performance of the popsicle stick bridges.

Video Clip: Popsicle Bridge Testing using a UTM at DLSU CE Lab

Structural Engineering for Kids 2 - Shaping Up Humpty Dumpty

You may be wondering why Humpty Dumpty fell from the wall if he has legs and hands. Well this is because of his shape which is very unstable. When he sat on the wall, he is not anymore supported by his legs and a little push will make him roll and thus he fell from the wall. If Humpty Dumpty is an inverted triangle, he will be more unstable. He will stand on the tip of the triangle and he has to balance himself otherwise he'll fall. But a rectangular or upright triangle- shaped Humpty Dumpty will be difficult to be overturned even if he is not supported by his two legs since the bottom side is flat for both shapes and the center of mass is near the bottom.

Shapes play a major role in the behavior of structures. Observed that because of the stable upright triangular shape, the Pyramids of Egypt and the Eiffel Tower have remained structural wonders. In earthquake design of structures, rectangular and upright triangular shaped buildings and towers are more preferred because of their regular shape. To build tall skyscrapers like the Taipei 101, the floor area has to be reduced as it goes up. An inverted triangle is the worst type of configuration for a building because it will behave like an inverted pendulum where the inertia forces will be concentrated at the top and there is very little resistance to lateral movements. The overturning moment will be too large such that it can easily be toppled down. Irregularly shaped structures, of course, can still be built provided they are properly modelled, analyzed and designed.

Structural Engineering for Kids 1- Humpty Dumpty & Structural Failures

Remember the nursery rhymes and songs your parents have read and sung for you just to put you to sleep? You or your parents may have not realized that when you were babies, you were unconsciously introduced to basic concepts of Structural Engineering whenever these nursery songs are played.

Humpty Dumpty sat on a wall

Humpty Dumpty had a great fall

All the king’s horses and

All the king’s men

Couldn’t put Humpty Dumpty

Together again

This nursery rhyme is a favorite of my two kids. It is a lesson on structural engineering failures and instability. The egg-shaped Humpty Dumpty is an example of an unstable structure. A little push will make it roll and fall. Similarly, buildings or bridges will be damaged or will collapse if they are not properly designed and built against expected forces. Proper design of foundations, detailed analysis of connections, and correct design of structural members are necessary ingredients against structural failures. Minor damages such as simple cracks may be acceptable but structures must not collapse, such that they are beyond repair endangering people's lives.

Inspired by the Humpty Dumpty music, I created a short video clip about the damaged buildings during the 1990 Luzon Earthquake. Humpty Dumpty here represents Luzon and its damaged structures. Perhaps, nursery rhymes and children songs may be a good way of introducing Disaster Awareness and Preparedness to kids.

The idea of this blog was inspired from Henry Petroski’s book, “To Engineer is Human.” Petroski argues that “the ideas of engineering are in our bones and part of our human nature and experience.” This is a good book specially for non-technical people who wants to understand concepts of engineering design.

Understanding Eathquakes& Disasters:Photo-Video

Computers and multimedia equipment have become popular tools in public presentations. In most conferences or seminars, a multimedia projector has become a common equipment. Recognizing this fact, the use of multimedia may be used for effective public awareness and education. However, there is a lack of multimedia software or presentations that are readily available for public use. It is for this reason, that I pursued the creation of photo-video presentations to be used in schools and public lectures. The photo-video presentations consists of photos or images integrated with text and music by a video editing software. The techniques and tools needed in producing personal multimedia presentations are discussed in a paper in my website: http://mysite.dlsu.edu.ph/faculty/oretaa.

“Understanding Earthquakes and Disasters: Photo-Video Presentations” is a project funded by the DLSU-Manila University Research Coordination Office (URCO). It consists of eight short presentations (watch the video clip below to know the 8 photo-video presentations) which can be played using a DVD player or a computer with Windows Media Player or similar software. The main focus of the photo-video presentations is the impact of earthquake hazards – ground shaking, surface rupture, liquefaction, tsunami, landslides – to the community and infrastructures. By presenting the effects of earthquakes, the public will understand their vulnerability to the different types of seismic hazards. And by knowing ones’ vulnerability, appropriate actions can be done to mitigate the adverse impacts of the hazards and avoid a disaster. Contact me if you want a copy of the presentation.

Introducing the 8 Titles in "Undertanding Earthquakes & Disasters: Photo-Video Presentations"

Building Popsicle Stick Bridges

I built my first popsicle stick bridge about 12 years ago when I was introduced to the bridge building contest organized by the students of the DLSU Civil Engineering Society (CES). My bridge was a through truss bridge. A through truss bridge derives its strength from the arrangement and strength of the truss elements. The load is transferred from the bridge deck to the truss elements and then to the supports. There are other types of bridge forms that can be created. A deck or girder bridge resists loads through bending – hence you must design the bridge deck such that it will have a large moment of inertia.The arch bridge, on the other hand, transfers the load to the abutments or supports through compression.

Bridge building is a fun and challenging activity. By applying basic strength of materials and bridge design principles, a little creativity and a lot of patience, you can create your own masterpiece similar to the CES bridges shown. So why not test your skills on popsicle stick bridge building by joining the 5th DLSU CES Bridge Building Competition? The competition is open to all civil engineering students in the Philippines. The best bridge design wins P5,000. The bridge with the largest “stiffness/weight ratio” wins P10,000. Check-out the rules in the ads shown in this blog site.

There are more postings related to popsicle stick bridge building and bridges in this blog. Go to this link.

Get some building tips at

http://claymore.engineer.gvsu.edu/~oostdykj/techniques.html.

Check-out http://pghbridges.com/basics.htm for various forms.

Photos of CES Bridges by Joenel Galupino: http://misfortunes.multiply.com/photos/album/60/MISFORTUNE_55

Introducing Damper Baby

Reducing building vibrations due to wind and earthquakes in tall buildings is one problem that must be addressed by structural engineers. There are various ways of doing this. One method is by installing passive and active dampers. When I visited Taipei 101 in 2007, I was introduced to “Damper Baby,” – the name given to one of the dampers installed at the currently world’s tallest building. Taipei 101 has a total height from the ground to the spire of 509 m. It has 101 stories above ground and five underground. In designing the tower, engineers had to consider the fact that " it will stand about 650 feet from a major fault line, and that it will face winds of 100 mph." Deflections resulting from extreme wind loads and earthquakes will be minimized by "three separate tuned-mass dampers: a primary, low-frequency 635,000kg damping sphere almost 6m in diameter formed from 41 layers of 12cm thick steel is suspended between the 92nd and the 88th floor to counter overall tower sway, while two smaller, higher-frequency dampers 7 tons in weight are installed inside the 20 m tall mast to counter mast vibrations. " The damper can reduce building vibrations by as much as 40%. Another technology of reducing vibrations is by the use of active control systems. Taipei 101 has also active control systems which eliminate vibrations. The video below is an exhibit at Taipei 101 showing the effect of active control systems in buildings.

Ref. http://www.allaboutskyscrapers.com/sp.taipei_101.htm

Riding the World’s Fastest Elevator at Taipei 101

I reached level 89 of Taipei 101 last June 2007 using the world's fastest elevator with a top speed of 1010 m/min (63 km/h or 37.5 mph) The ride from B1 to the observation deck at level 89 was comfortable and took only 39 seconds. The elevators installed by Toshiba contain pressure control systems which adjust the atmosphere inside to prevent ear-popping. Taipei 101 is currently the official world’s tallest building, but come 2009, Burj Dubai in UAE with 141 floors will claim this title once its construction is finished. Observatory elevators with speeds of 18m/s (40 mph) will be installed at Burj Dubai. With fast elevators like this, it will take less than 2.5 min to go up the conceptualized 2.4 km tall Dubai “Vertical City” Tower! Read my blog on "Reaching for the Sky". Reference: http://www.allaboutskyscrapers.com/sp.taipei_101.htm and http://www.burjdubai.com/

Reaching for the Sky

Concept designs of skyscrapers that will solve the problem of the future – the need for housing, work and entertainment place for a growing population in a limited space – have been proposed. In Discovery Channel’s “Engineering the Impossible,” the concept and challenges in designing and building a 2,755 ft tall and 170 story Millenium Tower to be built at the middle of the ocean in Hong Kong in 2050 was presented. Recently, an architect’s design of a 2.4 km (1.5 miles) high Dubai City Tower also called as the Vertical City is circulating in the internet. The proposed tower which is to be sited along the Persian gulf will have a total of 400 stories. For every 100 stories, there are Sky Plazas connected by vertical bullet trains. The building would be fitted with solar panels and wind turbines, and biospheres that double as recreational parks and water purification centers. The challenges in building these skyscrapers are numerous. The major problem is safety – will they be able to withstand wind and earthquake forces? Then there is a need for voluminous amount of construction materials for a gigantic structure. Next will be the construction technology and manpower required. And finally the services needed to support such height – transportation, water, power and waste disposal. Could they really be built? Photos from (http://www.realtyna.com/dubai_real_estate/dubai-city-tower.html)

GREAT TEACHERS - Joedec and Doc E

I have met two professors in civil engineering who possessed utmost enthusiasm and passion in teaching. The first one was Joedec, the late Prof. Jose Ma. De Castro of the University of the Philippines College of Engineering. JoeDec was my professor when I was pursuing my BSCE undergraduate course at UP Diliman. He was my professor in the Structural Engineering series subjects – CE53, CE54, CE55 and CE 56. JoeDec is a teacher who comes to class fully prepared with his teaching paraphernalia and up-to-date information about the subject. It was from him that I was introduced to the three basic tools in structural analysis – equilibrium, constitutive and compatibility equations in CE53. I still remember our exam in CE54 where we were asked to analyze a trapezoidal-shaped RC section – that was not easy! It was in CE55 that we were first introduced to the state-of-the-art computer-aided structural analysis using computer cards and main frame computers. In CE56, he taught us special topics like design of col-formed steel sections and analysis of footings on elastic foundations. I have never understood everything Joedec taught us, but I was inspired to study hard. Joedec never earned a PhD degree but with his vast knowledge in various topics in civil engineering, he deserves one!

The other CE professor is Prof. Romeo A. Estanero who retired in December 2007 after more than 21 years of teaching at De La Salle University – Manila. Prof. Estanero or popularly known as Doc E was not my professor but he is a colleague in the profession. He was the CE Department chair when I applied for a teaching position at DLSU in 1994. I have observed Doc E when he delivers his lectures in the classroom and in conferences - it was informative, lively and full of animated body language. His whole body is a teaching aid – he bends, sways, wiggles when he teaches topics such as buckling behavior of columns or traffic loads in bridges. He is innovative and up-to-date in his teaching. He uses models and posters in structural design courses. He enhances the teaching of RC design through laboratory destructive testing of concrete beams. Doc E used computers effectively in the classroom via powerpoint presentations and spreadsheet computations. I can still remember when Doc E had a mild stroke - he just took a one month sick leave and then continued his teaching at DLSU until his retirement - that's dedication! Doc E, although he has retired from teaching, continuously inspires young students and engineers in various CE seminars.

Joedec and Doc E are two great and outstanding Filipino professors in civil engineering. For them, teaching and learning are lifelong endeavors.

Video: Doc E talks about Bridge Design Principles at the CES Bridge Seminar held at DLSU last Oct 11, 2008.

20 Years of Civil Engineering at DLSU - Manila

In 2007, the Department of Civil Engineering of De La Salle University – Manila (DLSU-M) turned 20. In SY 1987 – 1988, through the initiative of Dr. Romeo A. Estanero and Dr. Angel Lazaro III, Dean of the College of Engineering then, the BSCE program was revived to produce qualified, specialized and research-oriented professional civil engineers. The DLSU-M BSCE curriculum pioneered the offering of specialization in Civil Engineering. The fields of specialization in Construction Technology and Management (CTM) and Structural Engineering (STE) were introduced in 1992, Hydraulics and Water Resources (HWR) in 1994 and Transportation Engineering (TRE) in 1995. Geotechnical Engineering (GTE) will also be offered soon. DLSU-M graduated its 1st batch of students in April 1991 and as of 1st Term SY2007-2008, there were about 854 Civil Engineering graduates. The DLSU-M Civil Engineering Family is very proud of its graduates who are now very much active in their chosen careers. DLSU-M CE Department also offers Master’s Degree programs, MSCE (Thesis option) and M. Eng (Practicum option) in all the fields of specialization.

I started teaching at De La Salle University - Manila in 1994 after earning my Doctor of Engineering in Civil Engineering from Japan. I served as the chair of the department for about three years. I feel proud to have shared my knowledge to many outstanding students who are now building their futures as professionals.

(Photo: The CE Faculty DLSU-Manila during the graduation last October 4, 2008)

Hey, La Sallian alumni civil engineers - share us your unforgettable moments and teachers during your stay at DLSU. POST your Comments!