Of course the association is wrong. The supports are undoubtedly part of the common (or at least limited common) area which is the association's responsibility. Their refusal to admit their responsibility is yet another example of idiots in positions for which they have no understanding of how condominiums work and are probably desperate to avoid having the association members (including themselves) assume responsibility for what is also undoubtedly an expensive repair that will probably increase fees or trigger a dreaded special assessment, not understanding that such is how condominiums are supposed to work. Unfortunately you are in a difficult position and, even though I usually hate recommending one seek the help of an attorney I suspect that is where you will probably need to go because the association's response is so outrageous. Good luck. I assume the Illinois condo act does define common and limited common areas and who is responsible for maintenance. Are you sure it doesn't?

I am going to suggest that the answer will not be addressed in the IL Condominium Act. Where I live, (NE), this question is not addressed in the Condominium Property Act. It is however, address most clearly in the Association Documents. 
Somewhere in your condominium documents there will be a definition of the common areas, the limited common areas and the units. In my condominium this is defined in a document called the Master Deed. In other states and associations, it might be in the original Declarations and CCRS, I am guessing, and unlikely to be in the By-Laws. Anything below the paint on the concrete slab my unit sits on is a common area.  
Your association board may or may not be correct. For starters have you begun communications with the board on repairs and have you and the association contacted the insurance company covering the damages? In my association, our coverage covers anything attached to the building including parts technically part of the unit owner's property (not common). 
And what has the association said about repairing the structural damage? 
I am going to venture an opinion that if the damage was done to failure of structural components in the common area, the association is liable for the repairs to your unit. (Not a lawyer). This is the most common situation but this opinion may be incorrect depending on language of YOUR condominium documents and your state law, which would be outside of the Condominium act. 
If I were you I would research this, and contact the insurance company, of the association, and your homeowners insurance company first. Make claims. Your insurance company has experts in this area and will try to pass the cost to the association if it has legal liability.

First, I find it hard to believe that what you have described is a condo. It sounds more like a townhouse because a condo with such a defect would affect the condo above you and condos never have a crawlspace. Therefore, I will assume townhouse in my response. 
 
You describe 'steel support column' issue which I have to assume only supports the structure above. Another assumption, there is no other owner property above you. 
 
In a townhouse, you, the owner, are responsible for everything vertically up to the roof, which if a continuous design from one of the structure to the other, covering more than just your townhouse would be considered a common area and a HOA responsibility. 
 
Should, at the base of the structure, there be a support structure that spans multiple townhouses. That is considered a common area and a HOA responsibility. 
 
There should be a firewall between your townhouse and the adjacent townhouses. That is considered a common area and a HOA responsibility. 
 
Bottom line, your responsibility to repair completely. In addition, if this defect impacts the roof structure, the HOA could bill you for its repair.

I assume you have insurance covering damage to your unit. Call your insurance agent and get your insurance company involved. I is their problem, not yours.

As Don said, get the insurance companies involved.  
But then there will be the question of who will cover the deductables... 
Our condo association has a policy with a $2000 dollar deductable so then the question is if that cost should be borne by the association or the unit owner.  
I read parts of the IL Condominium Property Act just now. A condo association is required to have coverage. And it says the definitions of common elements should be in the Declarations, so the OP needs to read those original and amended Declarations.

Ron- I have lived in two condos. Both have crawl spaces. Both crawl spaces are defined in the "Master Deed" (called "Declaration" in Maine where I now live) as limited common areas, with the association responsible for maintenance. Think it very hard to believe that this situation is the responsibility of the unit owner regardless of what state is involved. But have no experience with a "townhouse" that is not a condo (my current residence is a condo townhouse).

Insurance covers "sudden and accidental" damage, not "sinking" buildings. If it happened suddenly one day, then ask them to cover it. They can also sometimes give you free legal information. 
 
If your association knew about the rot, under your unit or other units, and they failed to take reasonable steps to inspect it and fix it, then the association is legally negligent and they have to repair your unit. The association is responsible for any damage that occurred to your unit after they knew about the problem. You won't find this in the Condominium law since it is part of property law and court case law.

From Wikipedia: 
 
A condominium, or condo, is the form of housing tenure and other real property where a specified part of a piece of real estate (usually of an apartment house) is individually owned, while use of and access to common facilities in the piece such as hallways, heating system, elevators, exterior areas is executed under legal rights associated with the individual ownership and controlled by the association of owners that jointly represent ownership of the whole piece. 
 
Colloquially, the term is often used to refer to the unit itself in place of the word "apartment". A condominium may be simply defined as an "apartment" that the resident owns as opposed to rents. 
 
http://en.wikipedia.org/wiki/Condominium 
-------------------------------- 
The name "townhouse" or "townhomes" was later used to describe non-uniform units in suburban areas that are designed to mimic detached or semi-detached homes. Today, the name townhouse is used to describe units mimicking a detached home that are attached in a multi-unit complex. The distinction between dwellings called "apartments" and those called "townhouses" is that townhouses usually consist of multiple floors and have their own outside door as opposed to having only one level and an interior hallway access. They can also be “stacked” and such townhouses have multiple units vertically (typically two), normally each with its own private entrance from the street or at least from the outside. They can be side by side in a row of three or more, in which case they are sometimes referred to as “rowhouses”. 
 
http://en.wikipedia.org/wiki/Townhouse 
-------------------------------- 
Beyond the actual dictionary definitions is the architectural code of the local and state governments. 
 
As to whether or not condos can have crawlspaces, that is dependent on local code. 
 
The initial description is of "steel support columns." Columns are usually vertical. So the question is, what are they supporting? I suspect the "steel support columns" are like those found in basements to hold up timber which spans a long distance to hold up the flooring or walls above, thus only affecting a single owner. To have another owned property above this is doubtful.

The master deed or declaration should clearly spell what common and limited common is and who is responsible for what.In our declaration in (CT) limited common items as they are described in our declaration are the responsibility of the individual unit owner.The key in the limited common definition is that it only affects you.If you have a unit above you and both units are being damaged it would be the the responsibility of the association to fix it.This a case where you should obtain all the necessary documents and have a condo attorney review them for you before it gets any worse.

Interesting point, Ron; It appears that who is responsible for the limited common areas 
may differ depending on the state and the declarations. In my association, limit common areas are maintained by the association, not the unit owner, even though they are for the exclusive use of a particular unit owner. 
Once again differences in law and documents makes it hard to give definitive answers but only more definitive questions.

I think I know where you live. There are 45 buildings and they all have the same issue. The management company runs the association and calls the shots. They say they are not responsible for the crawl spaces. They don't want to pay for the repair and that is the bottom line.

It is instructive to google "Illinois Limited Common Elements" I learned that one feature is to give control to the board, and that in the declarations, responsibility for maintenance can be transferred to unit owner tied to the element.  
 
 
Limited Common Elements - variably defined: 
Limited common elements is a term that is heard and used without a real understanding of what it means. Limited common elements and common elements are terms that identify physical components of property. Although the term limited common elements is used in many instances, to describe parts of property, the definition and the term is a condominium definition and term. Limited common elements are defined in the Condominium Property Act ("Act") at Section 2 (s). Section 2 (s) states: "Limited Common Elements" means a portion of the common elements so designated in the declaration as being reserved for the use of a certain unit or units to the exclusion of other units, including but not limited to balconies, terraces, patios and parking spaces or facilities." 
 
Section 2.1 of the Act states that the provisions of the Act are applicable to all condominiums in the state; and that any provisions of a condominium instrument that contains provisions inconsistent with the provisions of the Act are void as against public policy and ineffective. Consequently, the definition for limited common elements that is present in the statute is a controlling definition. It supercedes any definition in any condominium declaration that is inconsistent with its wording. Any provisions in a declaration that are inconsistent are void as against public policy. 
 
That does not mean that all definitions in a declaration are void. Many of the definitions, and many specifics in definitions or in declarations that further define limited common elements may not be inconsistent, but may be further definitions or identifications of specific limited common elements that are considered to fall within the definition of Section 2(s). Those further definitions are not inconsistent with the Act. The Act itself further identifies general and specific limited common elements at Section 4.1 (a)(5). This Section is entitled "Construction, Interpretation And Validity Of Condominium Instruments" and states: 
 
(a) Except to the extent otherwise provided by the declaration or other condominium instruments - - (5) any shutters, awnings, window boxes, door steps, porches, balconies, patios, perimeter doors, windows, and perimeter walls and any other apparatus designed to serve a single unit shall be deemed a limited common element appertaining to that unit exclusively. 
 
Thus, specific portions of property in a condominium are as a matter of law, and by definition, limited common elements. However, it is again noted that these definitions control only to the extent that the declaration or other condominium instruments do not otherwise define these components. To the extent the declaration does not otherwise define these components, they are limited common elements. 
 
Limited common elements are a specific defined type of common element. The Act at Section 2 (e) defines common elements. It states: 
 
"2 (e) "Common Elements" means all portions of the property except the units, including limited common elements unless otherwise specified." 
 
Because the limited common elements are also common elements, all of the general rights and obligations associated with common elements apply to limited common elements, except to the extent otherwise specifically provided or applied in the Act, and except to the extent specified in the declaration or other instruments. 
 
Section 4 of the Act identifies in outline form those things that should be in a declaration. At paragraph (g), it provides that the declaration should include: 
 
(g) A description of both the common and limited common elements, if any, indicating the manner of their assignment to a unit or units. 
 
Although that statement is specified in Section 4 of the Act, in many condominium declarations there is no detailing of the common elements or the limited common elements. Only the definitions are given. 
 
It is important to remember that common elements and limited common elements are always under the direct supervision and control of the board of directors of the Association. That means the board can limit or control their use, operation, maintenance, and repair, but again subject to any limitations that exist in the Act, and any limitations or requirements in the declaration. For example, boards can control what can be placed on balconies and patios even though they are limited common elements. They can control what is done with, on or in limited common elements such as, for example prohibiting barbecuing on balconies. They can prevent windows and doors and window trim from being painted, covered, or modified. Of course, no modifications may be made to limited common elements unless approved or authorized by the board. 
 
The board must maintain this control. It does not make a difference what physical characteristics of the property exist. This control is fundamental in condominiums. The board will be in breach of its duties if that control is not maintained. 
 
Although the board exercises control and authority over the limited common elements, the unit owner that has a particular limited common element is entitled to the exclusive use and enjoyment of that, limited common element. Again however that is subject to the board' s control, the owners proper use as a limited common element, the declaration requirements and rules and regulations applicable to the limited common element. Typically for example, a limited common element parking space is utilized only by the owner to whom it is assigned. It is only used for parking a car. A balcony or patio is utilized as a balcony or patio only by the unit owner to whom it is assigned. Obviously, windows, doors and peripheral parts of units are for the exclusive use and benefit of the unit owner. They cannot paint them, decorate them or cover them except as allowed by the board. 
 
Another important reason for defining limited common elements is to allow transfer of the responsibility for the cost of maintenance or repair of a component to the owner. Clearly, if a limited common element is damaged or destroyed by an owner as a result of an intentional or negligent act or omission, that owner is responsible for the cost of maintenance and repair associated with the damage or destruction caused. That is basic law. Now many declarations also transfer maintenance, repair and replacement, or the cost of maintenance, repair and replacement, to the unit owner to whom the limited common element is assigned. The declaration can identify specific limited common elements such as doors, windows, and window components that are to be painted, maintained or repaired, at the expense of the individual unit owner, or by the unit owner, subject to the rules, requirements, limitations and controls of the board. Similarly, the declaration can specify other limited common element maintenance and repair to be the responsibility of the unit owner to whom that limited common element is assigned such as parking spaces, balconies and patios. Alternately and/or in addition, the declaration can specify that the board has the right to decide whether the maintenance, repair or replacement of any one or more of the limited common elements is to be at the expense of the unit owner, or by the unit owner; or whether it should be a common expense to be paid by the association. The declaration can provide that the board may have discretionary authority to decide who is to pay for or perform maintenance, repair or replacement for each limited common element. In this case, the board can exercise its discretion separately with respect to each limited common element. 
 
In each case, the declaration wording will control. The board must follow that wording. If the declaration allows, the board can tell the unit owners that the cost of painting the front door will be charged to each separate owner or will be a common charge. It can also tell each owner that the cost of replacing a door or performing any repairs on a door is the unit owners expense. 
 
As noted previously, the board can have the owners perform maintenance, repair or replacement on limited common elements. However, it is important to know all such authorizations are completely subject to board authorization and approval of the specific work; the board's right to oversee and supervise the work, the board's right to require that the work is done in accordance with their policies, procedures and standards; and by competent trades people that are insured and that have provided insurance certificates to the Association, in accordance with Section 12 of the Act, naming the association as an additional insured. The fact that an association may authorize unit owners to do repair and replacement does not give the owner absolute or unlimited authority or power to do as they wish in the repair or replacement, or do it by themselves. Should a unit owner proceed in a fashion that is not acceptable, the Association can and should require removal of whatever was done that does not comply, and require replacement with what is allowed or authorized. 
 
The limited common elements that are identified in declarations are parking spaces, balconies and patios. Fireplaces within a unit would be considered to be limited common elements if they serve only a single unit, as well as the chimney for that fireplace however they are seldom identified. 
 
Boards can and should consider creating a list of items that would be limited common elements, and other items that would be common elements. It should further consider establishing policies as to which limited common elements are to be maintained at the expense of the association, and which are to be maintained at the expense of the individual unit owner. To the extent that the Association is either obligated to require the unit owner to maintain, repair or replace limited common elements, or authorizes the unit owner pursuant to the declaration provision to maintain, repair or replace; the association should establish standards and guidelines for that work including authorized and approved contractors, authorized and approved replacement components and materials, and a form that must be completed by the unit owner and approved by the board before the work is performed. Again do not forget to require the work to be performed by an independent contractor that is insured and provides a certificate of insurance to the association, naming the association as an additional insured. 
 
The one limited common element that is most often identified in declarations is parking spaces that are assigned to unit owners. If there are parking spaces assigned that are separate and separately identified, and that are not attached to a unit (such as individual garages or individual parking pads in front of individual garages); those other types of parking spaces must be transferred in accordance with the requirements of the declaration and also in accordance with Section 26 of the Act. There are very specific requirements set forth in Section 26 for transfer of limited common elements, which must be followed in order to effectively transfer a limited common element. Normally, parking spaces that are limited common elements spaces are assigned to a particular unit. They are listed as a limited common element assigned to that unit in a deed conveying the unit. The declaration may say they pass with title to the unit. In that case, when the unit is sold, the deed selling the unit should also assign that parking space. However, if the parking space can be separately assigned, it must be done before the sale of the unit and in accordance with Section 26 of the Act. 
 
Limited common elements can add much flexibility to associations boards and unit owners' rights and responsibilities. However, they are still limited common elements and the board is charged with exercising responsibility over them and over every unit owners use of that property. 

I am not sure this will get read, but here goes: 
1)Any national Insurance company will issue an endorsement to your Condominium HO-6 policy that will cover the Condo Master Polity deductible if you are reponsible for the deductible. Cost is dirt cheap, like $1.00 per year per $1,000 deductible.  
2. In Washington state the Condominium Declaration (CC&R) has to state specifically that the unit owner is responsible for the Master Policy Deductible. If the CC&Rs do not state that specifically, then the CC&Rs have to be amended to include it.  
3. Normally the Association is responsible for maintenace, repair and replacement for everything outside the unit, UNLESS the Declaration says different.