The architecture, is the story of space and time, it is about fashion, colors, natural light, and nice views. It is also about a fresh breath of green and positive interfacing with the community, all of which pour in pride of owning an apartment in a landmark building.

On the other hand, structural engineering is the language of architecture; it is the words or vocabulary through which architecture is written. Some of this "vocabulary" is quite eloquent and makes a powerful impact, as seen in the Sydney Opera House here in Sydney, or the Burj Dubai. Others stumble, like those rectangular apartment buildings we see everywhere, the majority of which are designed by nothing but greed. I am not quite sure if there is ever architecture in those other than complying dimensions or sometimes performance solutions. I only see rectangles stacking next to each other, above each other, to form giant rectangles, or sometimes trapezoids when the land has such shape.

Let us face it, there is a huge need to grow, and a great demand by our communities to expand and aspire. At the same time, we live in a world of limited resources and increasing awareness of human's footprint on the environment and nature. That said, can we not agree on common grounds? And when I say "we," I mean us in the built environment, the architects with the developers at their back, and the structural engineers, the deliverers of the whole vision.

Developer A and Developer B

Let us say we have Developer A, who instructed the architect to design a building to have, say, 100 apartments, a mixture of 1 bedders and 2. The developer's motive is to achieve meaningful feasibility of their project after buying land for many million dollars, in an area that sells at $10,000 per square meter. The construction cost nowadays is anywhere between $25 and $60 hundred dollars, depending on the quality of finishes and the tier of the builder. In simplest terms, the architect's task will be reduced to achieving the highest possible count of apartments, and this probably comes after fierce competition with other architects who say we can do more (race to the bottom?). We then come to the podium levels where we need to add some communal spaces and retail spaces to sweeten the deal, and down under, we search for every possible space to fit parking spots in.

With this come nasty things, to name a few:

• Several major transfer slab levels, above the parking levels, and above the podiums, and also through the building height because the apartments will not line up or stack as we need to squeeze more units or meet certain compliance, etc.
• Rotating staircases (yes, those spider stairs that take a certain direction in the basement to maintain the aisle at 5.8 meters, then rotate 90 degrees at ground floors, and rotate again 90 degrees at level 1 before picking up several mini stairs from the stepping podiums, etc).
• Some stairs start from the transfer ground level, others get lucky to reach the foundation level.
• Few lifts start from level 1 because we don't need them down under.

Then it might dawn on the designer that the clear heights will not be achieved unless the transfer is not exceeding a certain depth, and consult with some engineers who, in turn, enter this crazy pursuit by trying to make it work (oh, I hate this statement), or doubling the amount of columns in the upper levels so the transfer loads get sweeter, etc, or maybe come up with other ideas like different column grid but within the same limited thinking. And at the end, after the whole crew of experts reaches conclusions and delivers a so-called complying design to the developer who did not expect to have the design in the criteria he has given will cost some 20% extra due to the understandably expensive structure and services. He probably thinks he has hired the wrong team and decides to export the problem by giving the project to the cheapest tier builder in town who cuts corners and works on very slim margins, to make the costs making sense. Over and above this, our very own government has privatised the whole approval process and certification since the 1990s and does not send inspectors to police construction sites progressively, but rather comes at the end after the whole thing is messed up and claims to be the good guy for the rescue, and blames the whole universe but itself, rather than being involved since the beginning and partnering with the players to protect the interest of its own citizens. The rest is very well known to all of us, we read all about it in the news every day with a pointless blame game that will result in nothing but more demand on the property market, without the purchasing power, rounds and rounds, until complete economic depression.

How many Developer A’s have we dealt with?

Now let us look at the Story of Developer B. This bloke has the same land and decided to achieve feasibility by delivering a high-quality product and came to the Architects asking them to come up with a design concept that will sell itself. The architect warned that they will not achieve 100 units, but rather 80. However, the 80 units will be selling at the price of 100 units since your developer B has a good portfolio, and we as architects are not motivated by the typical greed seen in Developer A space.
The architect here decided to give the building a character, provided some curves and edges, and given nice facades that fit well within the environment. Also was mindful of so many other things like wider corridors, good search pattern parking floors without cul-de-sac, better accessibility conditions not shaved all dimensions to the bone. Thought well of insulation and suggested double glazing with central air conditioning on the roof (I can't believe we still have split units in Sydney at the balconies or hung on the elevations, unless architects like to see them as a feature?). The structural engineers receive the vision well, and since nothing invites for unnecessary design gymnastics, unless they serve for an artistic purpose that gives the building its value and character, the structural system makes a lot of sense, and becomes very economic, within say 20% of the building cost, and due to simplicity it becomes easy to build and everybody is happy, including the environment, economy, and the community wide.

In conclusion

The tales of Developer A and Developer B underscore the critical juncture at which architecture, engineering, and development intersect. Developer A's story exemplifies the pitfalls of prioritizing quantity over quality, driven by short-term gains and competitive pressures. Meanwhile, Developer B's narrative showcases the potential for a more holistic approach, where innovation, sustainability, and community engagement drive the creation of enduring spaces.

As we navigate the complexities of urban development, it's essential to heed the lessons embedded in these stories. By fostering collaboration among architects, developers, engineers, and policymakers, we can chart a course towards a built environment that not only meets our present needs but also enriches the lives of future generations.

Ultimately, the legacy we leave behind is not just in bricks and mortar but in the intangible qualities of beauty, functionality, and harmony that define our shared spaces. Let us strive to build not just structures, but vibrant communities that stand as testaments to human creativity and resilience.

Hey folks,

Although I’ve been in the business of structural engineering for over two decades, and despite being a chartered member of IStructE, a UK accreditation body, I only knew about the Irish Structural Engineer, Peter Rice, a few years ago! I said to myself, alas! What am I doing? This rush in doing work and attempting to be up to speed with industry commitments made me miss great things… This dilemma of balancing between acquiring knowledge while servicing clients and employers keeps coming up along the way, and whenever I meet a great mentor or know about an inventive piece of work.

I remember experiencing similar feelings early on when I knew about Nervi, Fazlur Rahman Khan, Ove Arup, Frei Otto, and even some of the living superstars like Bill Baker and Robert Sinn, however, Peter Rice struck me the most!

For those who don’t know him, it can be safely said that he was, and still, one of the greatest minds in structural engineering, a true thinker and compassionate human being who invented so many beautiful things that we take for granted.

Peter Rice’s book, An Engineer Imagines, presents so many ideas and memories shaped Peter’s character and inventive thinking. Starting from early years at school, thorough experience in Sydney Opera House, and the projects with Piano and Rogers, not to mention the Fiat experience (yes, the car maker), until the Moon Theater, the same venue he celebrated his daughter’s wedding in.

Great things are in the book, some here:

• The Iago mindset: This character which is borrowed from Shakespeare’s Othello play. In simplest ways, Iago used very logical arguments to service an evil agenda which has led to Othello killing his beloved one. We engineers sometimes put ourselves in the scene just like Iago, by presenting so many logical, or conservative, propositions to kill the spirit of the projects we work on. For example, insisting on a certain load path, contradicting with the geometry or the function we are dealing with. Imagine this mentality was there since the beginning at the pioneers' age? We could have missed seeing the greatest structures that challenged the status quo at the time. Engineering education is supposed to arm us with knowledge and tools to sail with the wind; however, we use this very education to set limits and stop thinking. This is undermining the very purpose of what we do. Engineers in the past used to be architects and builders, free from the current distinction they draw around themselves nowadays. Peter spoke about this in person when he received his gold medal of RIBA, see this video.
• About Jean Prouvé: Interesting is how we value education above everything and assume it giving a license to build. Jean was a true thinker and inventor, like the pioneers, who held the grip of what he did and presented solutions like a genius. Some individuals have a great engineering sense or ability to see the analysis and design without numbers at all, and others are at the opposite side, can’t do nothing without punching digits or modeling nowadays. However, very few are able to merge between these two lines of thinking.
• Centre Pompidou and Lloyds building: probably the most famous two buildings designed by Peter. Both complement each other and as he described, they are two sides of one coin. In the former, he used the cast iron “gerberette” and in the latter, used precast brackets out of circular columns. Peter loved these two, probably the most, I will leave it to you to read.
• Peter spoke a lot about how to deal with the dominance of industry and skepticism of builders etc.. a true challenge we are always faced with.
• The Pavilion of the Future of Seville: This is probably one of the most interesting engineering pieces of work. I am fascinated by this structure, will write a dedicated text to talk about it. Meanwhile, you will find STONE arches, roughly 35 meters tall, balanced laterally by cables and steel tubes, and made “prestressed” by taking the load of the building behind. I would never think of a design like this in a million years. Read this link1, and this link2.
• The Fiat Experience: yes Fiat the car maker. Will leave this for later.

It would be good to start these reflections with the following quotes (Wilson, Jan 2002):

[My freshman Physics instructor dogmatically warned the class "do not use an equation you cannot derive". The same instructor once stated that "if a person had five minutes to solve a problem, that their life depended upon, the individual should spend three minutes reading and clearly understanding the problem"..."With respect to modern structural engineering, one can restate these remarks as "do not use a structural analysis program unless you fully understand the theory and approximations used within the program"]

It has been quite a while since starting my career; through which, I have attempted, or more precisely, life has taken me across a number of challenges, in a pursuit for engineering excellence that I hope would be reached one day. One of these dares is trying to track, or maybe confirm, the actual development in structural engineering, in light of the astronomical advancement of #CAD / #FEA and debate of responsibly deploying them. A debate usually witnessed among young and “older” professionals.

Let us imagine a journey in time, no farther than the late 1970’s; maybe similar discussions on the analysis and design aids were, as well, very much on the table. Examples include the use of ready design charts like column interaction diagrams versus establishing case-specific ones, or crack width tables for water-retaining structures, #Pucher_Charts for plate elements, and helical stairs analysis charts, etc... The older chaps back then used to, most probably, criticize the heavy reliance on these things “without understanding the basics”, albeit many of them now pride themselves on the ability to use the “old fashioned” charts versus “blind” #FEA software packages, by suggesting that using them is more sensible.

We have been living the same debate, and we will continue to do so. Yes, we see every day those who analyze deep beams as elastic shell elements, or even by applying WL^2/8 to design them, and yes, some analyze seismic excited structure with little or no information about basic vibration theory. We come across many of those who claim to design according to certain codes and in reality, they simply change the design option in the software without reading the code itself or having a copy of it. But after all, there are great engineers who attribute lots of their experience and development to FEA-provoked ideas and techniques.

It is not disputed that #FEA method has participated in expanding our theoretical knowledge and efficiency. For instance, we have a more accurate appreciation of materials behavior by modeling the non-linear parameters virtually without having to do full-scale testing; we can resolve n degrees of indeterminacy in no time. We have a much better understanding of the external loads applied to our structures; we can simulate them without shaking tables. We've recently started to consider adopting performance-based design (#PBD) over strict reliance on codes. Some have already ditched the inertia reduction factors suggested by seismic codes and found several ways to calculate them accurately. Others discovered that the “weak storey” doesn’t apply for the floors below and above Outriggers in Outrigger-braced Supertall buildings (Choi, Hi Sun, Goman Ho, Leonard Joseph, and Neville Mathias, 2014). Moreover, the #FEA use is evolving; we started to reconsider the deployment of existing analysis techniques like response spectrum analysis and have NL #time_history as a standard approach instead. We could very soon have topology optimization as a fundamental tool in every project. All of this has been made possible by the power of computers and #FEA, these horses that we ride extremely well sometimes, and awfully bad most of the time. In short, we must acknowledge that we are learning so much by interacting with #FEA packages. Something like putting the hands on a #Ferrari wheel for the first time, you must be trained, sluggishly at the beginning, until mastering it. You will later admit that you have never been a driver up until sitting on that red leather seat!

But here is the big question: Are the majority of structural engineers getting really better? I guess not at all, the overwhelming situation is worrying. There is a whole generation of structural engineers who can't make a single step without ETABS, SAP, RAM, and SPACE GASS, etc.. This is why it will be inevitable one day to enforce formal certification for using software packages. I guess we will see -in the future- licensed FEA Engineers pledged to abide by a code of conduct and committed to CPD in FEA particularly, just like #Chartered / #PE engineers around the world.

On a separate note, I guess the public see things in a simpler way: designers now, and in the past, are just the same, how can we say that is not true if we stand next to the 9-decades-old #Empire_State? It is undoubtedly a great engineering task, designed and completed in mere 20 months (S Ghosh, K Robson, 2015) with no, whatsoever, any aid of the advanced #FEA packages we wear on our heads every day. Is that a valid claim? Obviously not, because if we design the very Empire State today, adopting the same lateral system, we would have accounted, to say the least, for the stiffness contribution of the cinder concrete encasement put around all of its steel frame elements (Taranath, 1998) without calculations. This encasement has increased the intended lateral stiffness by 4.8 times. Taranath says: “The structural steel frame with riveted joints, while encased in cinder concrete, was designed to carry 100% of gravity and 100% wind load imposed on the building. The encasement, although neglected in strength analysis, stiffened the frame particularly against wind load. Measured frequencies on the completed frame have estimated the actual stiffness at 4.8 times the stiffness of the bare frame” (Taranath, 1998, p. 10).

Moreover, the same building today would have been designed for the accurate application of horizontal loads, followed by proper analysis and optimization. Not only this, it could have been provided with more efficient lateral systems without fearing the complex analysis and try-error cycles by hand.

To #FEA or not to be? I am sure you know the answer, but let us regulate it at least within our professional organizations, until there is something formal one day in the near future.

---

Works Cited

Choi, Hi Sun, Goman Ho, Leonard Joseph, and Neville Mathias. (2014). Outrigger Design for High-Rise Buildings: An Output of the Ctbuh Outrigger Working Group (2 ed.). New York: Routledge.

S Ghosh, K Robson. (2015). Analyzing the Empire State Building Project from the Perspective of Lean Delivery System—A Descriptive Case Study. International Journal of Construction Education and Research, 1-14.

Taranath, B. S. (1998). Steel, concrete, and composite design of tall buildings. New York: McGraw-Hill.

Wikipedia. (2018). Empire State Building. Retrieved June 1, 2018, from https://en.wikipedia.org/wiki/Empire_State_Building

Wilson, E. L. (Jan 2002). Three-Dimensional Static and Dynamic Analysis of Structures (3rd Edition ed.). Berkeley, California, USA: Computers and Structures, Inc.

Designing columns is possibly the most repetitive task structural engineers undertake in their daily routine. When we have a column subject to combined axial and bending, one might ask the following questions:

1. How slender is this column?
   Slenderness of any column is the single most important parameter we should determine at the beginning of the design task. As a rule of thumb, if the column is braced, then a height to width ratio (or slenderness) under 15 should make an axially loaded column fail at a loading nearing the squash load, i.e., the capacity of the section. Whereas in unbraced floors, the height to width ratio should not be any greater than 10; otherwise, failure will happen quickly on buckling way before the section capacity is suffering.
   Keep in mind 3 ratios: N*/BH, M1*/BH², and M2*/HB²; if the first one is above 15, then have a closer look, and if any of the other two is higher than 1.5, do the same! Also, make sure you are watching the moments applied at top and bottom; if they are resulting in single curvature deformation, then have a good check!
   Talking about braced or unbraced floor, or column, is also a very interesting topic! Providing a concrete core or shear wall does not tick the box, and we still need to make sure that the floor in question is sway or not. This can be easily checked by calculating if the following ratio (from ACI318-M): Q = (SP x D) / (V x L) Where SP is the sum of axial loads in the floor, D is the lateral sway from the same load scenario, V is the lateral load applied onto the floor, and L is the storey height. If Q is less than 5%, then the floor is column/floor deemed to be braced.
   When a floor is sway, which is not a good thing, we are entering a totally different league because the failure at buckling becomes really problematic, imagine that if you have a column of circa 3 meters in height, will have to be studied as 4.5 or 5 meters… too bad.
   In any case, braced or not, we need to calculate the Euler load of the column, that is:
   
   This is a Frankenstein version of the original Euler load which addressed steel columns, or more specific a material does not suffer cracking or load redistribution like concrete. So what our code writers did, they’ve invented a moment-curvature formula linking the inertia with concrete strain and moment capacity at the balanced condition (i.e. the highest moment capacity of column that coincides with some 30% of maximum axial load).
   Also when you look at this Nc equation, you will find that the higher is the sustained load on the column, the lesser is the capacity, something really interesting and eye-opening! When we talk concrete we need to count for cracking AND creeping.
   RKALC will help on this, and will determine each and every meaningful ratio:
   
2. Is there a problem in 3D? (Biaxial Moments)?
   In simple words, we need to study an interaction somewhere between the two for each axis, or under a performance point = (N,Mx,My) and this can be looked at in the Pink diagram of RKALC.
   Note the code formulae here is nothing but an equation of an ellipse, that becomes a circle at maximum, or a triangle at minimum. It is very interesting to see that the bi-axial capacity becomes less "triangle" when the column is subject to low axial loading, becomes high, or like a circle equation, when the axial load is high.
   
3. How does it perform under fire?
   The Australian Standard gives good guidance on columns performing under fire; however, the method there is very crude and does not give full context on the assumptions. This is why we all use the Eurocode 1992-2, which is fully permitted under the Australian Standard.
   Basically, we apply the full dead load and a fraction of the live, and check if the column is subject to small, moderate, or high first order moment, then interpolate between nine tables C1 to C9 to determine the minimum width of the column.
   Our standard has taken tables C4-5-6 assuming moderate first order moment; this is why we do not use it unless the analysis shows moderate.
   RKALC is able to do the interpolation for you, using the EC2-2.
   
4. Does it need special confinement reinforcement?
   When the high-strength concrete is subject to high axial load or high bending, confinement becomes paramount; this is something you need to maintain near the junctions when the column is subject to double curvature moments, and within the centre height when single.
   RKALC is able to study this seamlessly:
   

STM is a very efficient and simple way to represent the stress flow within a concrete element or parts of it that are under the D region category, where Bernoulli assumptions are not applicable. Some say that the use of this method goes back to the early 20th century, yes, some 120 years ago when concrete was a new thing, and engineers used to rely on their intuition and expectation of load path.

STM was given several boosts between the sixties and early eighties when Schlaich et al. published guidance on the theory and given typical examples with load paths. Later, international codes started to implement and “regulate” it if you wish, to keep up with engineers, who always challenge the status quo.

In recent decades, computers have developed astronomically, to an extent that simulation of cracked concrete and non-linear analysis are becoming a standard. More interestingly, the load path is now easy to find via Topology Optimisation software packages, yet STM remains indispensable despite being a lower bound type.

Typically, you would start with a certain model or triangulated load path and assume truss as well as node depths, then draw geometry and analyze to check the stresses and reinforcement. This cycle keeps repeating until reaching reasonable convergence, i.e., stresses are slightly above code limits to claim the maximum truss depth for minimum REO percentage.

Clearly, it is tiring and needs to be automated somehow; hence, the RKALC’s STM calculator.

General rules to follow:

1. The concrete structure is basically divided into either B (Bernoulli) regions where the beam theory applies and stress distribution is linear within the section, or D (Disturbed) regions where it doesn’t.
2. Within the D regions, truss analogy can be applied by following the load path lines (principal stresses) and representing them as straight struts (compression members - concrete) and ties (tension members - reinforcement) intersect in nodes (concrete).
3. The angle between diagonal Struts and the horizontal line is feasible between 25º and 65º.
4. Equilibrium must be maintained while developing the STM model, and concrete must not fail before the steel reinforcement yields.
5. Tension is neglected in concrete, and forces in struts are uniaxial.
6. Anchorage and detailing are essential.
7. There is no exact STM model; however, there are poor and good models.
8. Struts can be categorized into prism, bottle, and fan.
9. Nodes (concrete) are categorized into 4 types: CCC, CCT, CTT, TTT (C stands for compression, and T stands for tension).
10. Stresses within struts, ties, support, and under load regions must be within allowable code limits.

Have you had a chance to explore our STM Calculator? (strut-and-tie method) Within its virtual walls, you'll discover a treasure trove of our most sought-after apps, each a shining star in its own right. These exclusive gems aren't just unique in the whole web – they're here to serve up engineering analyses and designs in a way that's nothing short of cutting-edge.

Meet the STM Wall app, a true time-saver when it comes to tackling iterative STM models. No more hours lost in geometry puzzles and stress calculations. With this app at your fingertips, you'll breeze through those tasks, giving you the freedom to focus on the finer points of your job and dive deep into detailed design processes. See Link

And that's not all – say hello to the RKALC Diamond app, your go-to guide for handling rotating columns with finesse. Imagine a column taking a 90-degree spin from basement to the ground floor. It's a sight to behold, and our RKALC Diamond app ensures that the transition is as smooth as sound. It helps you size up a column capital if needed, directing stress across a three-dimensional domain and channeling reinforcement through the column cores, creating a solid foundation for strength. See Link

Last but certainly not least, our Corbel app is your passport to perfect corbel creation, employing the Schlaich STM model. Just like its companion app, this tool lets you dive deep into the specifics of corbel design, sizing up nodes and selecting the ideal struts to ensure structural harmony. See Link

So, what are you waiting for? Embark on a journey through our suite of apps. It's more than just grim and boring calculations – it's about transforming your engineering experience to the KALC way where again, you put face to the KALC.

First things first, as you read this post, please refer to Coupled Shear Wall calculator available at: See Link

The issue of coupled shear walls is one of the most debated topics among structural engineers. It's not surprising to see five people with twenty different opinions, each of valid points. Ove #Arup once said on this:

"The more you look, the more you see,
And that's why experts disagree.
For some look here, and some look there,
But no one can look everywhere.
For if they did, it seems to me
That they would hardly be experts, you see.
According to their point of view,
What they say may well be true,
But looking from another angle,
We tend to get into a tangle.
Which of the views is then correct?
That is not easy to suspect.”

Many of us might appreciate that the flexibility of the beams can affect the distribution of force within height. There's an old rule of thumb that states coupling beams experience maximum shear within the bottom quarter of the wall height (around 0.2 to 0.3 of H). According to a wise man by the name Juravski, a rigid beam takes shear represented by Vh/z. Here, V stands for the total shear applied to the wall, h represents the typical storey height, and z is the ratio of the wall length in plan (0.7L for single walls and approximately 0.85 for walls forming part of the core).

In cases where the geometry doesn't allow for squat-like or stiff beams with minimum depth and the span is relatively large, we refer to this as a flexible beam with an aspect ratio greater than, let's say, 4 (span to depth). In such scenarios, the maximum force travels from the bottom quarter to approximately 0.5 to 0.7 of H, resulting in a fairly uniform distribution of force across all beams. The magnitude, in this case, becomes a fraction of Juravski's formula, roughly ranging from 30% to 50%.

There's also a sweet spot, a range of medium stiffness with an aspect ratio between 2 and 4. Within this range, the shear suffered is approximately 75% of Juravski's formula, occurring at 30% to 50% of the height.

In any of the three cases mentioned above, the total sum of shears taken by the beams would be equal to the total reaction exerted by the wall pier connected to the group of beams.

It is unfavorable to have no coupling beams and solely rely on the slab as the coupling element. However, there may be situations where space constraints force such a configuration, and in those cases, the global behavior of the wall can be manipulated by transferring the force from one level to another.

Irrespective of beam depth or rigidity, some of us try to make sense of what we observe in ETABS. For instance, when adjusting beam stiffness to 40%, 70% etc., we are addressing a relevant matter. This involves artificially simulating post-ultimate loading event behavior by inducing cracking, a matter of judgement and thinking. Try all of these scenarios at our RKALC calculator.

Clause 10.3.1 of the Australian Standard AS3600-2018 includes a very interesting stipulation on columns in relation to the ratio of M1/M2. This applies to normal columns found throughout the building height, which are typically subject to double curvature behaviors.
According to the Standard, if the analysis moment is less than the minimum eccentricity moment about the respective direction or 5%DN*, the ratio above should be taken as negative. This means the column should be assumed to be subject to single curvature, making it more conservative due to the high moment magnifier (δb).
The logic behind this stipulation is that there may be inaccuracies or errors during installation or due to pattern loading. As a result, the column might experience single curvature loading or "snap through to single curvature mode," as stated in AS3600. Therefore, the analysis assuming double curvature moments would be overwritten by the opposite minimum eccentricity moment.
You might think that increasing the analysis moment above the minimum would result in less conservatism, which is bizarre! However, there is a slight problem with this logic. If there are out-of-position issues, the column would most likely remain subject to single curvature mode, regardless of the analysis moment. This is because an increase in axial load due to construction tolerances or severe pattern loading will induce single curvature.
For those who follow the letter of the Standard rather than its spirit, it is always advisable to have the ratio negative. However, if you can justify it by rationalising the moments from analysis to capture pattern loading or out-of-position scenarios, you may consider otherwise. Ultimately, the judgment is left to your discretion.
Visit our very popular and free Column Calculator in following link, we have added saving and opening files to the webapp to save time of re-entering parameters.