HEC-RAS evolution

Some months ago, the new version of HEC-RAS version 5 with 2D capabilities was released. HEC-RAS is one of the most popular hyodynamic models. In this post I will provide a fast summary of the different versions of HEC-RAS.
HECs
Figure 1. User interface of HEC-RAS v1 (a) and HEC-RAS v5 (b)
HEC-2 or version 0
In 1968, the U.S. Corps of Engineers released HEC 2, the first American computer program for computing water surface profiles in channels with irregularly shaped cross sections. This program was written in Fortran and was able to calculate water surface elevations by solving the conservation of energy equation with the same iterative method used by HEC rras. The user interface was just a console screen with numbers and letters. Alothough it was not officially a HEC rras, I mention it as version 0 because its algoritm is the core of HEC rras.
Version 1
The first version of HEC-RAS was released in 1995, with a very basic user interface. I have the idea that this basic user interface is a key element for the high popularity of HEC-RAS. It is a simple, yet easy to understand interface. A comparison between the first interface of HEC-RAS and the interface of the newest HEC-RAS shows that there was little change in the interface (Figure 1).
Version 2
In the late 1998 HEC-RAS version 2.2 was released. The Federal Emergency Management Agency states that the most significant changes of this version were the crrections in bridge and culvert modeling. The previous versions of HEC-RAS inconectly calculated conveyance through bridges and culverts in pressure flow situations. Specifically, the problems occmTed in the momentum equation calculations for bridge analysis and in distinguishing between inlet and outlet control situations for culvert analysis. In general, culverts analyzed with HEC-RAS Version 2.2 under pressure flow will show lower water surface elevations than previous versions ofthe model. However, bridges analyzed with Version 2.2 under pressure flow generally show higher water-surface elevations using this version compared to previous versions ofthe model.
Version 3
In January 2001 the HEC-RAS version 3 was released. The main innovations of this release were the capabilities to perform unsteady flow simulations and the introduction of GIS with GeoRAS. HEC-GeoRAS changed the methodology for entering the geometric data and presenting results. Unsteady flow capabilities and GIS capabilities increased the range of applications and changed forever the way of showing results. Now, it was possible to show flood maps instead of just water profiles.
Version 4
In March 2008 HEC-RAS version 4 was released. The most significant modelling improvements of this version were the capabilities for sediment transport modelling and water quality modelling. New buttons were included to the graphical user interface: 1 button for quasy-unsteady flow conditions, 2 buttons to enter sediment and water quality boundary conditions and 2 buttons to perform the water quality and the sediment transport simulations. Besides, this was the first version that included the rras Mapper, which is the rras own GIS tool. Now, HEC-RAS does not need any external GIS software for showing flood maps.
Version 5
In February 2016 HEC-RAS version 5 was released. This was a very expected release. Not only because of the 2D capabilities, but also the release of the beta version in 2015 increased the expectation and the rummors about this new version; the social media and the internet forums were fulled with comments about this new version. The first scientific publication using this new 2D capabilities became available also in February 2016 (using the beta version). Personally, it is personal honor to be the author of such publication and I hope that it can be useful for future studies.
RAS-icons.png
Figure 2. Old HEC-RAS icon (Version 1 to version 4) and new HEC-RAS icon
 
Video. Animation of results with HEC-RAS v5

Soil challenges in the airport of the future (Mexico)

The airport of the future
Last year it was announced the construction of the Mexico city new international airport. Not only it will be one of the world's largest airports but it will also be the world's most sustainable airport and the first airport to be LEDD Platinun certified. As a matter of fact, it was called the "airport of the future" and "an inspiration for future airports".

The design of the airport was inspired by Mexican architecture and symbolism and was created to evoke a feeling of flight. The airport will honour the Mexican flag's coat of arms, which is a reference to Tenochtitlan, the pre-Columbian city on which the capital is built.

Image 1. Mexico City new international airport
Source: MexDF

The design and construction of this airport present special and unique challenges. The site for the new airport is located on the bed of the former Lake Texcoco. During the rainy season large sections of this area are inundated for several months and the soft soil conditions combined with ground water extraction result in large settlements. It is reported that some parts have already sunk some 5 meters since 1960. In order to deal with such challenges several engineering and technological innovations were required. In the present article we will discuss a little about the soil challenges (other features will be discussed in further articles).

Soil challenge
Mexico city and surrounding areas are located in what used to be a shallow lake (Texcoco lake). Thus, there is unstable soil with high water content and little capacity and the area is literally sinking. This poses extraordinary challenges for the design of structures. In the case of Mexico city new airport, this soil unstability posed two main problems: runways and terminals.

Runways
Six runways are planed for the new airport, each will be about 4 km long concrete topped embankments. In order to overcome sinking problems, each runway will be over a pile based deep foundation combined with polystyrene and other light materials.

Terminals
The initial design was composed of two terminals connected by a railway. However, a railway was not a good alternative because in such unstable soil conditions tracks will bend or move. Thus, engineers decided to modify the initial idea by one spectacular six million square feet terminal (560 000 sqm). This will be the second biggest airport terminal in the world (Hong Kong terminal one 570 000 sqm). Besides, in order to ensure a very light building engineers decided that the whole terminal would be enclosed within a continuous, lightweight grid shell that embraces the inner layers of the building and seamlessly acts as both its walls and roof. Combining both skin and structure in a single system, the shell stretches from the fixed boarding bridges to the top of the roof. For better understanding, it as a series of interlocking shell structures that resist their loads through in-plane forces - rather than bending - and are, as a consequence, extremely lightweight. Moreover, such kind of structure does not require false work or scaffolding, it can be erected much faster and more economically with fewer materials and less energy than ordinary buildings.

Image 2. Inside of terminal


References and further reading
Airport of the future in Mexico.
Mexico City's new airport: an inspiration for future airports
NACO wins a multi-million euro tender to design the airside infrastructure for Mexico City's new airport

Forceeffect: A structural analysis Application

A structural analysis software

Usually engineers rely on structural analysis software for the analysis and design of any type of structural system. Nowadays there are several structural analysis software products. Among the most popular ones we can mention SAP2000, ETABS, RAM, STAAD pro or ROBOT. However, such softwares have a high computing cost (so do an economic cost) and need to be run on computers at the office. Thus, it is difficults for the field engineer to perform some fast calculations. In the last years smart phones and tables changed the ways we use computers. Everyday new smart phones and tablets application are available. Application with engineering application are not an exception. Some years ago popular enginnering software like AutoCAD and ESRI ArcGIS became available as online applications. Now structural software application joined the list. 

Figure 1. Sample bridge project.
Source: Forceeffect

Autodesk Forceeffect

Some time ago Autodesk released Forceeffect, a free application for structural analysis. Autodesk Forceeffect allows creating a structure with different types of support, different elements and subject to different forces. Then, it shows how the forces are distributed over the elements and the stresses the elements are subject to. Moreover, the user can easily modify the structure by just drag and drop the elements of the structure and the results are automatically updated. If this is not enough, the user is able to save and to generate html from the design. Moreover, in order to improve the presentation of the results Forceeffect also allows importing a background image to base the design. The following images show the application of Forceeffect for design of a bridge (Figure 1) and a backhoe (Figure 2). There are 16 sample projects and a users community. Forceeffect is free; the user only need to create an Autodesk account (in case is not a member yet) and sign in. The following video shows an introduction to Forceeffect.

Figure 2. Sample backhoe project
Source: Forceeffect



Video 1. Introduction to Forceeffect

Further reading & references